***
If you're not sure this is actually a bug, instead post about it at https://discuss.kde.org

If you're reporting a crash, attach a backtrace with debug symbols; see https://community.kde.org/Guidelines_and_HOWTOs/Debugging/How_to_create_useful_crash_reports

Please remove this comment after reading and before submitting - thanks!
***

SUMMARY

I have an NVIDIA RTX 3090 and I just upgraded to Kubuntu 24.10 and tried HDR. Cycling HDR works fine while logged in but if I leave HDR on SDDM works fine but logging into a plasma wayland session causes my monitors to go black with no mouse cursor. Sounds happen if I plug or unplug devices leading me to believe the DE is still running but there is no display. Ctrl+Alt+F5 or similar does not work to give me a terminal. If I login through SSH I can restart SDDM using systemctl and SDDM will work properly (ie graphics capabilities restored,) but the logging into a plasma session will cause the issue to repeat. I originally fixed the issue by rolling back to nvidia-driver-550 turning off hdr and then reinstalling nvidia-driver-560. I also tried nvidia-driver-555 in the course of my troubleshooting and it seems to function identically to nvidia-driver-560 ie the problem exists and rolling from 555 to 560 or 560 to 555 doesn't help. 


STEPS TO REPRODUCE
1.  install Kubuntu 24.10 using nvidia-driver-560 or 555 using an nvidia graphics card
2.  log into a plasma session and enable hdr on all monitors
3.  restart the machine and try to log back in (I have not tested but assume logging out and logging back in would do the same)

OBSERVED RESULT

plasma session appears to be running but no graphical output is available and virtual terminals cannot be accessed with Ctrl+Alt+Fkey shortcuts.

EXPECTED RESULT
plasma session works normally and hdr is on.

SOFTWARE/OS VERSIONS

Linux/KDE Plasma: Kubuntu 24.10
KDE Plasma Version: 6.1.5
KDE Frameworks Version: 6.6.0 
Qt Version: 6.6.2

ADDITIONAL INFORMATION

I created a shell script so I can restore an image without switching drivers (I couldn't find a config file to change?,) by sshing in from another machine. 

#!/bin/env bash
WAYLAND_DISPLAY=wayland-0 #this will likely work for any normal desktop user might have to confirm the 
#environment variable in a working login session
kscreen-doctor output.DP-1.hdr.disable #I have two displayport monitors connected need to confirm monitor names
#in a working environment using "kscreen-doctor -o"
kscreen-doctor output.DP-2.hdr.disable