Before describing my issue, I installed the Nvidia drivers using these steps:
# apt install linux-headers-amd64
# apt install nvidia-open-kernel-dkms nvidia-driver firmware-misc-nonfree
I did not do any dracut configuration, because my system uses the regular initramfs-tools package. I did not add the options nvidia-drm modeset=1 line to /etc/modprobe.d/nvidia_options.conf, because I don’t want to use the Wayland session.
^These are the steps I followed as per the Debian Wiki
When I had an AMD GPU, SDDM would render properly at a my monitor’s 180Hz refresh rate. After entering my password, Plasma simply loaded up in a blink, without any flickers. Now SDDM renders at, I would say, 30Hz. After logging in, my screen goes black for about 2 seconds before Plasma shows up (the monitor’s power light indicates a complete loss of signal). After that everything is fine.
I am using Debian Trixie on the 6.12.38+deb13-amd64 kernel with the 550.163.01-2 Nvidia drivers. SDDM’s version is 0.21.0+git20250502.4fe234b-2 and Plasma’s is 6.3.6-1, but I don’t have any issues with Plasma at the moment.
Is there anything I could do to fix this petty inconvenience? Do I need to reconfigure X somehow? I suspect that Plasma uses xserver-xorg-video-nvidia as its driver, but SDDM uses software rendering somehow?