Hello! I’ve been wrestling with this for a few hours and finally fixed an issue. My secondary monitor rated at 1080@75hz would only do 60hz. If you pushed it to 75 the screen would go black and say unsupported mode. I tracked this down to an Nvidia proprietary driver. Anything past nvidia-510xx will cause this issue.
Best way to fix is to yay nvidia-510xx-dkms nvidia-510xx-utils and let it remove anything from the 515 branch we are on. However, this WILL NOT work with kernel 6.0+
So linux-lts or linux-tkg of 5.15 kernel was the way to go just make sure you update the grub entries before you restart with:
grub-mkconfig -o /boot/grub/grub.cfg
Once in that 5.15 kernel I could install the 510xx dkms nvidia driver and bang I am back to 1080@75hz on my second monitor.
I mainly wanted to post this for anyone else out there googling the same issue banging their head against a wall.
edit: spelling