Oh dear.

Dollars to donuts it was https://invent.kde.org/plasma/plasma-workspace/commit/13057013d55ae19e76d29b9edc96510e52da2a7a or https://invent.kde.org/plasma/plasma-workspace/commit/697b103f5fad5b40b207eabcbce162d6672f5d91.

Can you please run `/usr/lib/x86_64-linux-gnu/libexec/kscreenlocker_greet --testing` in a terminal window and attach the full text output? it will tell us the exact error.

Thanks for the quick response.

After running the suggested command I get the same black screen without the identification window, plus the following information:

$ /usr/lib/x86_64-linux-gnu/libexec/kscreenlocker_greet --testing
OpenGL vendor string:                   Intel
OpenGL renderer string:                 Mesa Intel(R) HD Graphics 530 (SKL GT2)
OpenGL version string:                  4.6 (Compatibility Profile) Mesa 20.2.6
OpenGL shading language version string: 4.60
Driver:                                 Intel
GPU class:                              Unknown
OpenGL version:                         4.6
GLSL version:                           4.60
Mesa version:                           20.2.6
Linux kernel version:                   5.4
Requires strict binding:                yes
GLSL shaders:                           yes
Texture NPOT support:                   yes
Virtual Machine:                        no
file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/lockscreen/LockScreen.qml:52:5: QML Connections: Implicitly defined onFoo properties in Connections are deprecated. Use this syntax instead: function onFoo(<arguments>) { ... }
Locked at 1617342572
file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/lockscreen/LockScreenUi.qml:233:26: Type MainBlock unavailable
file:///usr/share/plasma/look-and-feel/org.kde.breeze.desktop/contents/lockscreen/MainBlock.qml:73:13: Cannot assign to non-existent property "cursorVisible"

-----------------------------------------------------------

The same thing happens to me on another computer with different specifications but with the same version of KDE neon and also upgraded to 5.18.7

I took a day off today but will make it my top priority to investigate and fix this tomorrow. So sorry for the regression, especially in the LTS release! :)

Thank you in advance for your dedication and effort.

A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/768

Git commit c4a3a4e5b974fb309a6da61252b2b830d2d90683 by Nate Graham.
Committed on 03/04/2021 at 14:53.
Pushed by davidedmundson into branch 'Plasma/5.18'.

Revert "[lookandfeel] Fix wake existing screensaver mode with key presses"

This reverts commit 13057013d55ae19e76d29b9edc96510e52da2a7a.

That commit set the cursorVisible: propety to true. However that
property only exists in the QtQuickControls 2 TextField, not the QQC1
version. We ported the lock screen to PlasmaComponents3 (which
internally uses QQC2) after Plasma 5.18, meaning that in the LTS
version, we still have a QQC1 TextField so this property does not exist.
Trying to set it causes a runtime error and breaks the lock screen.
FIXED-IN: 5.18.7.1

M  +3    -0    lookandfeel/contents/lockscreen/LockScreenUi.qml
M  +0    -6    lookandfeel/contents/lockscreen/MainBlock.qml

https://invent.kde.org/plasma/plasma-workspace/commit/c4a3a4e5b974fb309a6da61252b2b830d2d90683

Perfect. I just updated the system and the bug is gone ;-)
Very good job.
Best regards.

Phew, glad to hear it! So sorry that this happened in the first place.

*** Bug 438498 has been marked as a duplicate of this bug. ***

*** Bug 438498 has been marked as a duplicate of this bug. ***