It seems there’s still a bit of work to be done, but it looks promising.

We are actively working on the remaining pieces to support D3D12 emulation via VKD3D-Proton. A lot is already done or in progress but there are still a few pieces missing, so don’t expect D3D12 games to work just yet.
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Performance is still a work in progress and continues to improve regularly. A lot of titles are running at 60 FPS or better on recent GPUs. With others, we’re seeing bottlenecks that we have yet to triage. If you want to know if your favorite game performs well, the best way is to just try.