I am just curious if anyone can give some insight into this? Many dx12 games (and many games don’t) work with Proton. What is missing in mesa or Proton to support the last dx12 bits?

Or is the reason actually somewhere else, some kind of middle ware?

I’m wondering because it seems like all, Vulkam. Mesa (radv) and Proton (vkd3d) supports more and more to be as DirectX compatible as possible, so how big is actually dx12 with regards to features that needs to be implemented in Vulkan/Proton/vkd3d/mesa to support everything?