This comment is meant to document my findings, Joshua told me he'll do the rest.

The game sets a float constant to infinity, which most likely causes issues with D3D9s funky floating point rules. The infinity is then multiplied with a value that's 0, which causes it to become NaN. Apparently D3D9 expects anything * 0 = 0.
9343501 @1 IDirect3DDevice9::SetPixelShaderConstantF(this = 0xc8e95a0, StartRegister = 0, pConstantData = [-inf, -0.000144277, 0, 0], Vector4fCount = 1) = D3D_OK
Should be fixed by c13395db970d16a5631a7c0926e2c4529d2710c3
proton 6.3-1x1 2021-04
When loading some maps nothing is displayed except the HUD.


DXVK
D3D9 Native
Software information
Red Orchestra 2: Heroes of Stalingrad with Rising Storm, ultra settings.
System information
Apitrace file(s)
Log files