I can no longer reproduce this issue on proton 8.0-3, proton experimental works too. I think there's a small graphical issue (at least on 8.0-3) but I'll test that later.
Opened an issue for the graphical issue https://github.com/HansKristian-Work/vkd3d-proton/issues/1688
Edit: it's apparently a game bug.
proton 8.0-3x1 2023-09proton experimentalx1 2023-09d3d12core.dllx1 2023-06
Compatibility Report
System Information
GPU: R9 380X
Driver/LLVM version: mesa git 23d4e21d835
Kernel version: 6.3.9 tkg
Link to full system information report as Gist:
Proton version:Experimental / 8
I confirm:
steam-2357010.log
Symptoms
Can't launch the game, an error window appears regarding DX12 and SM6.0 support

I saw these errors pop up in he terminal during prefix creation step:
But the files are there, so this might not mean anything.
Reproduction
Clicking play