This is a wine bug, the DXGI implementation is missing functionality for this game. It (kind of) works with a standalone d3d12.dll build combined with the DXGI implementation from DXVK.
As I understand, I need to build on Windows to get a standalone .dll?
no, but you need mingw to cross-compile on Linux.
You can use DirectX 12 with the latest RC of Proton 5.0-10. You just need to add the environment variable WINEDLLOVERRIDES=dxgi=n in order to use DXGI from DXVK.
Performance is impressive (not too different from d3d11), but with more stutter.
I however have a glitch where some lights have wrong color and power. It seems to be a bit random as affected lights aren't always the same.

Same issue with both RADV and AMDVLK.
Closing as it's a wine bug.
proton 5.0-10x1 2020-07proton 5.0x1 2020-07WINEDLLOVERRIDES=dxgi=n`x1 2020-07d3d12.dllx1 2020-07
Launching Hitman 2 with
DirectX 12crashes the game after pressing Play.Tested with
Proton 5.0.9with and withoutACO.Proton log: https://gist.github.com/FaithLV/3ecbbc04d0f4c2fd010019d28fd2e949
System Information
AMD FX-8300
RX 590
5.7.6-zen1-1-zen
Full Information: https://gist.githubusercontent.com/FaithLV/c3e0bb9bf3d02b2d42220e3ad984b7f0/raw/d94e1ce3582da67a2ead11222630bfc56693800a/steam-system