Thank you for the bug report! Unfortunately the backtrace is incomplete and missing debug symbols for the following lines that we need to figure out exactly what's going wrong:

#4  0x00007f672c5fe236 in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kscreen/KSC_KWayland.so
#5  0x00007f677198c7ea in ?? () from /lib/x86_64-linux-gnu/libffi.so.8
#6  0x00007f677198b923 in ?? () from /lib/x86_64-linux-gnu/libffi.so.8
#7  0x00007f6771ec3661 in ?? () from /lib/x86_64-linux-gnu/libwayland-client.so.0
#8  0x00007f6771ebfa0a in ?? () from /lib/x86_64-linux-gnu/libwayland-client.so.0

Could you please install debug symbols for kscreen, libffi, and likwayland-client, reproduce the crash, and attach a new symbolicated backtrace? See https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports

Thanks again!

(In reply to 281587887a from comment #0)
> SUMMARY
> Application: Plasma (plasmashell), signal: Segmentation fault
> 
> [KCrash Handler]
> #4  0x00007f672c5fe236 in ?? () from
> /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kscreen/KSC_KWayland.so
> #5  0x00007f677198c7ea in ?? () from /lib/x86_64-linux-gnu/libffi.so.8
> #6  0x00007f677198b923 in ?? () from /lib/x86_64-linux-gnu/libffi.so.8
> #7  0x00007f6771ec3661 in ?? () from
> /lib/x86_64-linux-gnu/libwayland-client.so.0
> #8  0x00007f6771ebfa0a in ?? () from
> /lib/x86_64-linux-gnu/libwayland-client.so.0
> #9  0x00007f6771ec132c in wl_display_dispatch_queue_pending () from
> /lib/x86_64-linux-gnu/libwayland-client.so.0
> #10 0x00007f676d90dc1b in QtWaylandClient::QWaylandDisplay::flushRequests()
> () from /lib/x86_64-linux-gnu/libQt5WaylandClient.so.5
> #11 0x00007f676fae6168 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
> #12 0x00007f676fb07193 in
> QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)
> () from /lib/x86_64-linux-gnu/libQt5Core.so.5
> #13 0x00007f676faae4db in
> QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from
> /lib/x86_64-linux-gnu/libQt5Core.so.5
> #14 0x00007f676fab67b0 in QCoreApplication::exec() () from
> /lib/x86_64-linux-gnu/libQt5Core.so.5
> #15 0x0000558a1210776a in ?? ()
> #16 0x00007f676f64a7fd in __libc_start_main () from
> /lib/x86_64-linux-gnu/libc.so.6
> #17 0x0000558a1210788a in ?? ()
> [Inferior 1 (process 27145) detached]
> 
> STEPS TO REPRODUCE
> 1. Have Debian testing installed on a PC with an NVIDIA GPU (using propriety
> drivers) 
> 2. Try to start Plasma with Wayland
> 
> OBSERVED RESULT
> Only black screen with the cursor visible, occasionally a bug window shows
> up, another window showing files and folders opens (Dolphin?) when you click
> on "Save".
> 
> EXPECTED RESULT
> A working system.
> 
> SOFTWARE/OS VERSIONS
> Linux/KDE Plasma: Debian GNU/Linux bookworm/sid x86_64
> KDE Plasma Version: 5.24.5
> KDE Frameworks Version: 5.94.0
> Qt Version: 5.15.2
> 
> ADDITIONAL INFORMATION
> nvidia-driver version is 470.129.06

Hi, I installed kscreen-dbgsym, libffi8-dbgsym, libwayland-client0-dbgsym, libwayland-client++1-dbgsym, and libwayland-client-extra++1-dbgsym. Here's the new crash report:

Application: Plasma (plasmashell), signal: Segmentation fault

[KCrash Handler]
#4  0x00007f6ceea96236 in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kscreen/KSC_KWayland.so
#5  0x00007f6d380d47ea in ffi_call_unix64 () at ../src/x86/unix64.S:105
#6  0x00007f6d380d3923 in ffi_call_int (cif=0x7ffead532160, fn=0x7f6ceea96210, rvalue=<optimized out>, avalue=<optimized out>, closure=<optimized out>) at ../src/x86/ffi64.c:672
#7  0x00007f6d39166661 in wl_closure_invoke (closure=closure@entry=0x7f6d24002710, flags=flags@entry=1, target=<optimized out>, target@entry=0x55b9a7876750, opcode=opcode@entry=0, data=<optimized out>) at ../src/connection.c:1025
#8  0x00007f6d39162a0a in dispatch_event (display=display@entry=0x55b9a5fc3600, queue=<optimized out>, queue=<optimized out>) at ../src/wayland-client.c:1583
#9  0x00007f6d3916432c in dispatch_queue (queue=0x55b9a5fc36d0, display=0x55b9a5fc3600) at ../src/wayland-client.c:1729
#10 wl_display_dispatch_queue_pending (display=0x55b9a5fc3600, queue=0x55b9a5fc36d0) at ../src/wayland-client.c:1971
#11 0x00007f6d34bc0c1b in QtWaylandClient::QWaylandDisplay::flushRequests() () from /lib/x86_64-linux-gnu/libQt5WaylandClient.so.5
#12 0x00007f6d36ee6168 in ?? () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#13 0x00007f6d36f07193 in QEventDispatcherGlib::processEvents(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#14 0x00007f6d36eae4db in QEventLoop::exec(QFlags<QEventLoop::ProcessEventsFlag>) () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#15 0x00007f6d36eb67b0 in QCoreApplication::exec() () from /lib/x86_64-linux-gnu/libQt5Core.so.5
#16 0x000055b9a3fb076a in ?? ()
#17 0x00007f6d36a4a7fd in __libc_start_main () from /lib/x86_64-linux-gnu/libc.so.6
#18 0x000055b9a3fb088a in ?? ()
[Inferior 1 (process 3147) detached]

We still don't have symbols for kscreen:

>#4  0x00007f6ceea96236 in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kscreen/KSC_KWayland.so
See where it says "?? ()" We need it to have something more than that.

(In reply to Nate Graham from comment #3)
> We still don't have symbols for kscreen:
> 
> >#4  0x00007f6ceea96236 in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kscreen/KSC_KWayland.so
> See where it says "?? ()" We need it to have something more than that.

I also installed libkf5screen-bin-dbgsym and libkf5screen7-dbgsym but failed to reproduce the bug report. I then did some updates via Discover, and saw that Wayland is working when I logged in. It could be updates or something else, I'm not sure. I'm marking this bug as resolved but if you want more information I'll be happy to provide.

(In reply to 281587887a from comment #4)
> (In reply to Nate Graham from comment #3)
> > We still don't have symbols for kscreen:
> > 
> > >#4  0x00007f6ceea96236 in ?? () from /usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kscreen/KSC_KWayland.so
> > See where it says "?? ()" We need it to have something more than that.
> 
> I also installed libkf5screen-bin-dbgsym and libkf5screen7-dbgsym but failed
> to reproduce the bug report. I then did some updates via Discover, and saw
> that Wayland is working when I logged in. It could be updates or something
> else, I'm not sure. I'm marking this bug as resolved but if you want more
> information I'll be happy to provide.

Well, looks like the issue persists. The updates apparently upgraded my kernel. With secure boot enabled, I have to sign nvidia kernel modules every time the kernel is updated. So Wayland worked because nvidia kernel modules were not loaded. ¯\_(ツ)_/¯

If you can now reproduce the issue again and yo also have debug symbols installed, can you paste the contents of a new backtrace that uses them?

Dear Bug Submitter,

This bug has been in NEEDSINFO status with no change for at least
15 days. Please provide the requested information as soon as
possible and set the bug status as REPORTED. Due to regular bug
tracker maintenance, if the bug is still in NEEDSINFO status with
no change in 30 days the bug will be closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

If you have already provided the requested information, please
mark the bug as REPORTED so that the KDE team knows that the bug is
ready to be confirmed.

Thank you for helping us make KDE software even better for everyone!

This bug has been in NEEDSINFO status with no change for at least
30 days. The bug is now closed as RESOLVED > WORKSFORME
due to lack of needed information.

For more information about our bug triaging procedures please read the
wiki located here:
https://community.kde.org/Guidelines_and_HOWTOs/Bug_triaging

Thank you for helping us make KDE software even better for everyone!