I meant the:

-force-d3d12

one. Might need to put "%command%" after it, but I'm still not 100% sure what that even means and why its there so I dunno.

Edit: I would also check out the entry for the game on ProtonDB if you haven't already (sorry if someone else has already told you all this elsewhere in the thread) to see if anyone else has had similar issues: https://www.protondb.com/app/949230

I haven't played C:S2 yet, so I can't say personally, but it could just be a poorly optimized game.

"Runs like shit" is expected when you're relying on paging to system memory every frame, step 1 is to avoid a crash from oom/failed alloc.

The next step is to reduce paging if possible. I see C:S2 has a min spec of a 4GB GPU. Assuming they actually tuned their game for such a card on windows, the unfortunate reality of proton/DXVK is that there's a bit of a memory overhead and lack of knowledge about residency priority, especially when translating a dx11 game.

DX12 maps to Vulkan more closely, so my hope is that the -force-d3d12 flag would give DXVK better info to work with (ex. hopefully the game makes use of dx12 heaps and placed resources, which are 1:1 with vulkan concepts, and dxvk can make use of that to better ensure the most important resources don't get paged out).