I had similar Problems. Ramdomly freezing of the desktop, start of a second sddm-loginscreen 5 minutes after login, graphical glitches in menue.
I always hoped that it woulöd get better after some updates. But (for what I can tell after 3 or 5 hours of testing afterwards) there where two things that made the system stable again:
- I switchted to another KDE-Plasma-Themes after I saw errors in journalctl refering to deprecated funtion calls in the theme I used. Now I’m back to one of the stock themes (beeze dark)
- For the flickering: It went way after I applyed this Kernel-Paramter found in this thread: Screen flickering on Linux kernel 6.12 - #17 by haykh
dcdebugmask=0x400