KDE Plasma shell black screen

[rubisetcie]

Hello KDE plasma core developer team, I hope you're having a nice day.

I'm trying to build KDE Plasma desktop *from source code* on Debian, using
the standard procedure based on kdesrc-build. While the building part went
very well, I'm stuck on the "*installation*" part: when I log in using
SDDM, I get the *loading screen then black-out with only my cursor visible*
...

I've tried everything to troubleshoot this to no avail (of course, the official
page <https://userbase.kde.org/Troubleshooting/Black_Screen> didn't help),
so I'm seeking help: *would you know what could cause KDE to black screen
when logging in?*

I will send you whatever informations/logs you may ask to help you
troubleshooting; I didn't find any obvious error in my "journalctl" (I'll
provide it if you request it, but because it's huge, I prefered to not
include it in this first mail).

Additional informations that may be important:

   - I'm trying to build KDE Plasma 5.27 on Debian 12 (branch group=
   stable-kf5-qt5).
   - I started from an installation without prior desktop: I do everything
   via TTY/SSH.$
   - Install prefix is "/opt/kde/" (I did made symlinks for executables to
   "/usr/local/bin", and stuff).

Thank you in advance, again don't hesitate to ask me if you need me to
provide you with some more detailed informations.
I wish you all a good continuation for your work.

Regards,
Matthieu 'Rubisetcie' Carteron
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