When I try (under bullseye) :
gtf 3840 2160 30xrandr --newmode "3840x2160_30.00" 339.57 3840 4080 4496 5152 2160 2161 2164 2197 -HSync +Vsync
xrandr --addmode HDMI-1 3840x2160_30.00 xrandr --output HDMI-1 --mode "3840x2160_30.00" the PC crashes (all is black, need to power off). Did anyone success in similar case..? Thnaks for any help. PC