@eugen-b, can you do a git-bisect between 1.20.11 and 1.20.12? You can use xorg-server-git PKGBUILD as base and change the source URL to _srcurl="git+https://gitlab.freedesktop.org/xorg/xserver.git#commit=COMMITSHA and use the shasum of the git bisect output replacing COMMITSHA as needed until you find the issue. Then post the findings upstream.
Almost the same. Optimus, hybrid mode, external monitor (via DP) works. I bet this is due to the difference in the way Nvidia connected to screen. My HDMI/DP are connected to Intel. Failed cases are likely with a connection to Nvidia directly.