

PROTON_HIDE_NVIDIA_GPU=0 PROTON_ENABLE_NVAPI=1 gamemoderun %command%

Unplayable with any Proton version. Some versions can produce 1-3 FPS
Any launch arguments will make the game not launch.
VKD3D_CONFIG=dxr11,dxr PROTON_ENABLE_NVAPI=1 gamescope -W 2560 -H 1440 -r 165 -f -- %command%

Get the infamous Unreal crash unless the game runs in Proton Experimental.
You need to run the game using Proton Experimental, otherwise it will crash when opening the first door. Once switched, I didn't notice any other problems.

Medium setting holds a comfortable 40 fps. Could probably max settings at 30 fps or with FSR/TSR/XESS at higher frame rate.

The game demo (you can expect the same behaviour from the complete game) works flawlessy once switched to experimental proton.
Lowered resolution to 1152x720 + FSR to achieve stable 40 fps at medium quality graphic

VKD3D_CONFIG=dxr11 VKD3D_FEATURE_LEVEL=12_2 %command%
Some stuttering, probably due to shader compilation or RTX.
Not sure if the commandline options are needed, I put them there to be sure I could use RTX. Note: I played the demo of Layers of Fear, not the final game.

Worked without a hitch. Just one crash in the settings menu.
Changed a setting in the gameplay menu which made the demo game crash.