An AMDGPU regression in 6.12
TL;DR Linux Kernel 6.11.10+/6.12/6.13 has AMDGPU regressions.
Add
Option "SWCursor" "True"
to/usr/share/X11/xorg.conf.d/10-amdgpu.conf
to resolve.Other's note
amdgpu.dcdebugmask=0x10
as a kernel parameter helps, didn't work for me.