Hi,
I am experiencing the same problem here (version 3.1.28.230805 using X11) and tracked it down. Problem is the call to gpgtar, which is generated by kleopatra to build the tar.gpg file. It is just broken:

gpgtar --batch --status-fd 23 --gpg-args --no-tty --gpg-args --charset=utf8 --gpg-args --enable-progress-filter --gpg-args --exit-on-status-write-error --gpg-args --display=:0 --gpg-args --ttyname=kein Terminal --gpg-args --ttytype=xterm --encrypt --sign --gpg-args --always-trust -r .... -u ... --output /tmp/test.tar.gpg --directory /tmp --files-from - --null --utf8-strings

The culprit is the option --gpg-args --ttyname=kein Terminal
kein and Terminal are separated - but they must be one part. Maybe a problem of the translation - don't know what name is used in English for the option --ttyname.

I "fixed" it by adding an own gpgtar file, which repairs the broken call before it is passed to gpgtar:

#!/bin/sh
tmp=`echo "$@" | sed -e "s/ --gpg-args --ttyname=kein Terminal//" -e "s/ --gpg-args --ttytype=xterm//"`
exec /usr/bin/gpgtar.bin $tmp

But there are many more problems:
- If you encrypt a tar.gpg file, the timestamps of all encrypted files are lost. They all have the actual timestamp. An error which has been fixed some time ago and now is there again.
- The directory structure is broken through decrypt. A given directory structure in tar of /1/2 is decrypted to /1/1/2
- Filenames seam to be interpreted during decryption. Therefore, some filenames can't be written to disk, because it's data garbage.

gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: warning: name not terminated by a nul
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: invalid octal number encountered - assuming 0
gpgtar: [?]: header block 2 is corrupt (size=0 type=10 nrec=0)
gpgtar: error creating '/raid/daten3/Transfer/Grafik/Sync/kleopatra-BRGyuw/Vattenfall/%PDF-1.7\n%����\n3 0 obj\n<</Length 2 0 R/Filter/FlateDecode/N 3/Range[0 1 0 1 0 1 ]>>\nstream\nx���wTS�\x16': Datei oder Verzeichnis nicht gefunden
gpg: error writing to '-': Datenübergabe unterbrochen (broken pipe)
gpg: handle plaintext failed: Datenübergabe unterbrochen (broken pipe)

Filenames leading to the above error are:
Arc_S_AUSWILL12226500100000DP20025020160103sapi2pci_I2P_401708914001236_3_Q1e6-1146.pdf.pdf
Arc_S_BLANK12226500100000DP20025020160103sapi2pci_I2P_401690808701147_Q4zk-20.pdf
Arc_S_BLANK12226500100000DP20025020160103sapi2pci_I2P_401721227200945_Q1-1180.pdf.pdf
Arc_ZVFE_JS_EZE01K650011251005222DP20024620160103sapi2pci_I2P_401723144142381_Q3m-352.pdf.pdf
Arc_ZVFE_JS_VBESTK650011251005222DP20024620160103sapi2pci_I2P_401704151142473_4_Q33k-432.pdf

The encrypt path seams to be working - I couldn't see any problem there so far.
kggpg can be always used to decrypt the tar.gpg files. It doesn't show the above described errors.

Andreas, thanks for identifying the cause of the original report.

Some remarks for the additional issues mentioned by Andreas Hartmann in comment #1:
> - If you encrypt a tar.gpg file, the timestamps of all encrypted files are
> lost. They all have the actual timestamp. An error which has been fixed some
> time ago and now is there again.

I doubt this ever worked with gpgtar, but in the past we have used tar+gpg instead of gpgtar and tar does preserve timestamps. Unfortunately, gpgtar doesn't. That's tracked by https://dev.gnupg.org/T5054.

> - The directory structure is broken through decrypt. A given directory
> structure in tar of /1/2 is decrypted to /1/1/2

This might be intentional. gpgtar never extracts to an existing non-empty directory. If that's not what you are seeing then file a ticket at https://dev.gnupg.org/.

> - Filenames seam to be interpreted during decryption. Therefore, some
> filenames can't be written to disk, because it's data garbage.

This looks like https://dev.gnupg.org/T4554. I created an archive with the filenames you listed (with gpgtar --create and copies of a random PDF file), but I could extract it without problems (with gpgtar --extract). Maybe encryption/decryption is required to trigger the problem.

I have no idea why on your systems ttyname is "kein Terminal" (or maybe the Spanish equivalent). The only explanation I have is that for some reason the environment variable GPG_TTY is set to this invalid value. If GPG_TTY is set then it must be set to a valid ttyname (i.e. a pathname like /dev/tty or /dev/pts/42) or the empty string, but it must not be set to "kein Terminal", "ningún terminal" or whatever.

Please check what value the environment variable GPG_TTY is set to.

Hello Ingo,
GPG_TTY is set to something like /dev/pts/[number] - that's the expected value. Tested in a pure konsole or in the konsole of dolphin.  Don't know where to search the origin of "kein Terminal".
I added a echo $GPG_TTY to my gpgtar helper bash script. At this point, the GPG_TTY env variable contains "kein Terminal". Don't know where it comes from.

The problem with directories during decryption can be seen, too, if the target directory doesn't exist at all. It's always directoryname/directoryname/ . For me, this behavior is just broken and doesn't make any sense.

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Andreas, thanks for the feedback. How do you start Kleopatra? Does the problem also occur if you start Kleopatra from Konsole? Make sure that Kleopatra is not still running (minimized in the system tray) when you try running it from Konsole.

The problem doesn't happen., if kleopatra is started in konsole before it is used. "Used" means: I do a right click to a file in dolphin, go to action and select decrypt / check e.g.
If I'm directly using the action decrypt / check before starting kleopatra manually, the problem comes up. Same problem happens, if  kleopatra is started via krunner before instead of via konsole.

I can reproduce the very same thing with kleopatra Version 4.0.0.241201 (24.12.1). GnuPG 2.4.5, Libgcrypt 1.11.0-unknown in Fedora 41.

If I try to pack and encrypt a folder from the dolphin service menu, I get the same error.
If I start kleopatra manually beforehand and then do the very same action from the dolphin service menu, it works.

Locale is also German, but I assume this happens with every locale where that translation contains a space.