PROTON_LOG
Writes a Proton and Wine debug log to $HOME/steam-<appid>.log. PROTON_LOG=1 enables the default channels. Maintainers ask for this log on almost every bug report.
PROTON_NO_ESYNC
VKD3D_CONFIG
WINEDLLOVERRIDES
PROTON_ENABLE_NVAPI
PROTON_USE_WINED3D
VK_ICD_FILENAMES
PROTON_HIDE_NVIDIA_GPU
PROTON_NO_FSYNC
DXVK_HUD
VKD3D_FEATURE_LEVEL
RADV_PERFTEST
WINEDEBUG