Wayland, hybrid graphics (16ACH6H) - passing video= yields flickering/artifacts on screen between boots

Following on from Plasma, Wayland, nVidia/AMD hybrid graphics - #4 by philstopford, I realized that I was only getting 60 Hz offered by the system. Under X11, I added a file under /usr/share/X11/xorg.conf.d so that I could use the 165 Hz refresh at 2560x1600.

Clearly, I needed similar intervention for Wayland. Hunting around, I found https://www.davejansen.com/add-custom-resolution-and-refresh-rate-when-using-wayland-gnome/ and that showed eDP-2 connected. So I set video=eDP-2:2560x1600@165 in the kernel command line and things start going wrong. On reboot, the screen retains artifacts from the previous session and these don’t go away even with a full power off. There’s also a lot of flickering and other weirdness. Removing the video= parameter, the artifacts persist until the system is powered down and left for several minutes.

This is evident from the system firmware screen through to the desktop. Nothing like this happens if I remove the video= parameter for Wayland, or at any refresh rate (60/165) under X11.

I wondered if anyone had some ideas about cause and options to mitigate this weirdness.