VKD3D-Proton (d3d12.dll and d3d12core.dll) loads the amdxc64.dll shim, which then loads amdxcffx64.dll when FSR4_UPGRADE=1 envvar is present. However, if you update the FidelityFX upscaler DLL ( amd_fidelityfx_upscaler_dx12.dll) and it has a newer build time than the “upgrade” DLL (amdxcffx64.dll), the upscaler DLL will be used to perform the FSR4 upgrade instead. Currently, the FidelityFX SDK 2.2.0 has a newer build time, so the “new” amdxcffx64.dll will not be used if you update the game’s FFX DLLs (upscaler and framegeneration DLLs). If FSR4_UPGRADE=0 or is not present, then amdxc64.dll will use the upscaler DLL for the FSR4 upgrade. In general, you do not need to use the Proton specific envvars to get the FSR4 upgrade to work, and can instead use the vkd3d-proton and amdxc64.dll envvars directly. The amdxc64.dll and amdxcffx64.dll files can be placed in the game directory next to the game executable or in the Wine system32 directory. To see if the upgrade is working you can set FSR4_WATERMARK=1 envvar and check the build time and compare with known build times to see which FSR4 version is being used. You can also use Wine debug channel amdxc to get more information: WINEDEBUG=-all,+amdxc,+loaddll.
To enable / disable the FSR4 upgrade without deleting or renaming any DLLs:
#FSR4 upgrade, will use the upscaler DLL
export WINEDLLOVERRIDES=dxgi,d3d12,d3d12core=n,b;amdxc64=b"
#have amdxc64.dll attempt to load the amdxcffx64.dll, the upscaler DLL may still be used if its build time is newer
export FSR4_UPGRADE=1
#stop amdxc64.dll from loading to prevent FSR4 upgrade
export WINEDLLOVERRIDES=dxgi,d3d12,d3d12core=n,b;amdxc64=d"
See my posts that explain this in more detail here: