I’m running a Radeon 6770 on my home machine, running Mint and running Baulder’s Gate 3 under Steam, and have been having some surfaces sparkle or not show correctly when running it with Vulkan in Proton, though everything looks perfect when using DirectX. It also looks correct in both modes when run on Steam deck. What is this phenomenon, just a bug in my graphics driver and Vulkan? None of my other games exhibit this issue.
The Steam Deck uses Wayland. Mint uses X11. That could be making the difference for the Vulkan version.
That and the 6770 is an old card, so it could be that the DX11 translated to Vulkan better takes your card’s particulars into account than the native Vulkan backend does.
This should be less the window server than the gfx API at play. I’d say force DirectX if you think that looks better visually.