SUMMARY
I also downloaded the 8.2.0 AppImage and tried to start it, which fails. Earlier versions did not have an issue (I'm currently using the 7.10 AppImage).

STEPS TO REPRODUCE
1. Download AppImage 8.2.0 on Debian 11.8
2. Start it in terminal

OBSERVED RESULT
Following error messages appear in the terminal:

$ ./digiKam-8.2.0-x86-64.appimage 
-- digiKam Linux AppImage Bundle
-- Use 'help' as CLI argument to know all available options for digiKam application.
-- Notes: to integrate this bundle to your desktop, use AppImageLauncher.
--        to enable all debug messages on the console, use 'export QT_LOGGING_RULES="digikam*=true"'.
--        to extract the bundle contents locally, use option '--appimage-extract' on the command line.
-- Detected host Linux -64-
-- AppImage mounted directory: /tmp/.mount_digiKa7HKWwK
Check library libudev.so.0
Check library libxcb-dri3.so.0
Check library libcrypto.so.1.1
Check library libssl.so.1.1
Check library libnss3.so
Check library libnssutil3.so
Check library libsmime3.so
Check library libgmodule-2.0.so.0
Check library libgnutls.so.30
-- Preloading shared libs: :/usr/lib/x86_64-linux-gnu/libxcb-dri3.so.0:/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1:/usr/lib/x86_64-linux-gnu/libssl.so.1.1:/usr/lib/x86_64-linux-gnu/libnss3.so:/usr/lib/x86_64-linux-gnu/libnssutil3.so:/usr/lib/x86_64-linux-gnu/libsmime3.so:/usr/lib/x86_64-linux-gnu/libgmodule-2.0.so.0:/usr/lib/x86_64-linux-gnu/libgnutls.so.30
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libMagick++-7.Q16.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libdigikamdatabase.so.8.2.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libdigikamcore.so.8.2.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libKF5CoreAddons.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libKF5ConfigCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libKF5Service.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_dnn.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_imgproc.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_ml.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_core.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_core.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_core.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libexiv2.so.28)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libheif.so.1)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libheif.so.1)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/liblensfun.so.2)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libopencv_imgcodecs.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libKF5ConfigWidgets.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libKF5KIOCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libKF5WindowSystem.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKa7HKWwK/usr/lib/libde265.so)

EXPECTED RESULT
Digikam starts without complaining about missing libraries.

SOFTWARE/OS VERSIONS
# uname -a
Linux myhostname 5.10.0-26-amd64 #1 SMP Debian 5.10.197-1 (2023-09-29) x86_64 GNU/Linux

ADDITIONAL INFORMATION
# ulimit -a
real-time non-blocking time  (microseconds, -R) unlimited
core file size              (blocks, -c) 0
data seg size               (kbytes, -d) unlimited
scheduling priority                 (-e) 0
file size                   (blocks, -f) unlimited
pending signals                     (-i) 256642
max locked memory           (kbytes, -l) 8219579
max memory size             (kbytes, -m) unlimited
open files                          (-n) 1024
pipe size                (512 bytes, -p) 8
POSIX message queues         (bytes, -q) 819200
real-time priority                  (-r) 0
stack size                  (kbytes, -s) 8192
cpu time                   (seconds, -t) unlimited
max user processes                  (-u) 256642
virtual memory              (kbytes, -v) unlimited
file locks                          (-x) unlimited

SUMMARY
In a Debian 12.4 VirtualBox virtual machine I downloaded the AppImage 8.2.0.

OBSERVED RESULT
It worked as expected

ADDITIONAL INFORMATION
$ uname -a
Linux debian12base 6.1.0-15-amd64 #1 SMP PREEMPT_DYNAMIC Debian 6.1.66-1 (2023-12-09) x86_64 GNU/Linux
VirtualBox 6.1.48 r159471 (Qt5.15.2)
VirtualBox Guest Additions: 6.1.48

Git commit 204529650237593450ea42ac7192ba2e2c17ef18 by Gilles Caulier.
Committed on 22/12/2023 at 12:12.
Pushed by cgilles into branch 'master'.

AppImage update frameworks:
Qt5   : 5.15.12
KDE   : 5.113
Plasma: 5.27.10
Kapp  : 23.08.4
Whole AppImage VM needs to be rebuild from scratch.
Related: bug 474265, bug 476092

M  +3    -3    project/bundles/3rdparty/ext_qt5/CMakeLists.txt
M  +3    -3    project/bundles/appimage/config.sh

https://invent.kde.org/graphics/digikam/-/commit/204529650237593450ea42ac7192ba2e2c17ef18

Hi all,

I rebuild whole AppImage from scratch under XUbuntu 18.04 includes all system updates. The VM was re-installed fully. There is no traces of older builds inside.

So the AppImage with this date (and later will be built on this VM : 20231222T162413

https://files.kde.org/digikam/

It uses internally last  Qt 5.15.12, and KDE framework 5.113.

The goal to use XUbuntu 18.04 guaranty a binary compatibility with Ubuntu* 20.x and later. 

So please download the bundle and try again.

Thanks in advance and Merry Christmas to all.

Best

Gilles Caulier

Thanks for your continuous efforts, Gilles!

I tested digiKam-8.3.0-20231222T162413-x86-64.appimage on Ubuntu 20.04.6 LTS and unfortunately without success, there are now even more error messages:

-- Preloading shared libs: :/usr/lib/x86_64-linux-gnu/libxcb-dri3.so.0:/usr/lib/x86_64-linux-gnu/libcrypto.so.1.1:/usr/lib/x86_64-linux-gnu/libssl.so.1.1:/usr/lib/x86_64-linux-gnu/libnss3.so:/usr/lib/x86_64-linux-gnu/libnssutil3.so:/usr/lib/x86_64-linux-gnu/libsmime3.so:/usr/lib/x86_64-linux-gnu/libgmodule-2.0.so.0:/usr/lib/x86_64-linux-gnu/libgnutls.so.30
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libdigikamgui.so.8.3.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libMagick++-7.Q16.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libdigikamdatabase.so.8.3.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libdigikamcore.so.8.3.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libKF5CoreAddons.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libKF5ConfigCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5Widgets.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5Core.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5Core.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libKF5Service.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5Xml.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_imgcodecs.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_dnn.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_imgproc.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_ml.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_core.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_core.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libopencv_core.so.408)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libexiv2.so.28)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libheif.so.1)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libheif.so.1)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/liblensfun.so.2)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5WebEngineCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5WebEngineCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libKF5ConfigWidgets.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5Network.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libKF5KIOCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libKF5WindowSystem.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libde265.so)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5Qml.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKamj2sA5/usr/lib/libQt5WaylandClient.so.5)

This i strange because it starts as expected with Ubuntu 22.04, 22.10, 23.94, and 23.10 here.

The reason why 20.x is not supported is obscures...

It 's work here on my Xubuntu 20.04 VM !!!
https://download.qelectrotech.org/qet/forum_img_2/digikam-8.3.0_appimage_20.04.png

I used debug AppImage...

@Gilles
https://download.qelectrotech.org/qet/forum_img_2/digikam-8.3.0_appimage_20.04-2.png

It strange that these plugins cannot be loaded. I will take a look.

Thanks Laurent to point me to this problem...

Gilles

Git commit 91b67530b3859acdc4820d36506ae50b3b4de6d7 by Gilles Caulier.
Committed on 23/12/2023 at 16:50.
Pushed by cgilles into branch 'master'.

Ignore Marble plugins in digiKam plugins loader, as Marble has a dedicated loader.
Related: bug 474265

M  +3    -2    core/libs/dplugins/setup/dpluginloader_p.cpp

https://invent.kde.org/graphics/digikam/-/commit/91b67530b3859acdc4820d36506ae50b3b4de6d7

You can find quite a lot about this problem on the web for other projects.
A possible solution to the test:

sudo apt update
sudo apt install build-essential

Maik

@ Maik:

Thanks for the tip, but:
build-essential is already the newest version (12.8ubuntu1.1).

Why should I install build-essential as an end user anyway? I thought the idea behind AppImages is that all necessary libraries get shipped with the program.

It's already the case, excepted the low level API C/C++ which still hosted in the system.

Git commit d690f6e70ffd2b1ee7fb1f21683e57fdc71edd45 by Gilles Caulier.
Committed on 09/02/2024 at 07:02.
Pushed by cgilles into branch 'master'.

adjust dependencies to compile AppImage bundle unde Ubuntu 20.06 CCBUGS:480134 CCBUGS:478222 CCBUGS: 474265

M  +2    -2    project/bundles/appimage/01-build-host.sh
M  +6    -2    project/bundles/appimage/host_ubuntu.inc

https://invent.kde.org/graphics/digikam/-/commit/d690f6e70ffd2b1ee7fb1f21683e57fdc71edd45

@Johannes,

The new digiKam 8.3.0 pre-release AppImage bundle for Linux based on Ubuntu 20.06 is now online at usual place:

https://files.kde.org/digikam/

Problem still reproducible with this version ?

Thanks in advance

Gilles Caulier

@Giles: Unfortunately yes. I think I'll have to update Ubuntu soon because other updated programs also started not to run under Ubuntu 20.04.6  anymore…

digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libdigikamgui.so.8.3.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libMagick++-7.Q16.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libdigikamdatabase.so.8.3.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libdigikamcore.so.8.3.0)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libKF5CoreAddons.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libKF5ConfigCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5Widgets.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5Core.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5Core.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libKF5Service.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5Xml.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_imgcodecs.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_dnn.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_imgproc.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_ml.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_core.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_core.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libopencv_core.so.409)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libexiv2.so.28)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libheif.so.1)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `CXXABI_1.3.13' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libheif.so.1)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/liblensfun.so.2)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.30' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5WebEngineCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5WebEngineCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libKF5ConfigWidgets.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5Network.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libKF5KIOCore.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libKF5WindowSystem.so.5)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libde265.so)
digikam: /lib/x86_64-linux-gnu/libstdc++.so.6: version `GLIBCXX_3.4.29' not found (required by /tmp/.mount_digiKaIXGp5E/usr/lib/libQt5Qml.so.5)

@Johannes,

Did you update your system and make a new try with the last AppImage bundle 8.3.0?

Best

Gilles Caulier

@caulier.gilles : 
Not yet.
I'm a farmer and the work outside started.
I'll report when I updated my computer.

AppImage bundle is now compiled with Ubuntu 20.06 and with Qt 5.15.13 and problem must be fixed. 
Reopen if necessary.
Gilles Caulier