I have a similar issue. When turning off the monitor using its power button, the system semi-crashes. After powering the monitor back on, I have to go into an alt shell and kill lightdm, which also kills all running GUI applications. Not the greatest workflow.
$ uname -a
Linux hostname 6.13.1-arch1-1 #1 SMP PREEMPT_DYNAMIC Sun, 02 Feb 2025 01:02:29 +0000 x86_64 GNU/Linux
NVIDIA-SMI 570.86.16
Driver Version: 570.86.16
CUDA Version: 12.8
Instead of powering off the monitor, I've created an alias:
alias off='xset dpms force off && await.sh && xset -dpms'
And shell script (press any key to unblank the screen):
$ cat ~/bin/await.sh
#!/usr/bin/env bash
xinput test-xi2 --root 2>&1 | \
grep --line-buffered -m 1 'EVENT type 2 (KeyPress)' &> /dev/null
This allows me to run "off", a comromise to put the monitor in low-power mode. This solves the problem of having to kill lightdm, which improves the workflow. Still, sometimes I have to open an alt shell and then press Alt+F7 to return to X. Rarely, I'll have to go to the alt shell/Alt+F7 a second time to suppress sporadic screen glitching.
Adding nomodeset to the GRUB configuration was another suggestion:
# grep vmlinuz /boot/grub/grub.cfg | head -1
linux /vmlinuz-linux root=UUID=... rw nomodeset quiet resume=UUID=...
Hope it helps.