It seems with FW there is now a fix that looks like it does fully eliminate these glitches, so only the VRR-related glitches seem to be left over: [amdgpu] Heavy artifacting in desktop applications since bump from 24.3.4 to 25.0.1 (#12809) · Issues · Mesa / mesa · GitLab
Install Linux 6.14 with Mesa 25.0.2 (no idea if that’s specific to that 25.x version) and in the BIOS settings, set the video memory to the game optimized 4 GB option.