CODE EXAMPLE FOR SHELL

run exe in proton prefix

cd /path/to/steam/steamapps/compatdata/20920/pfx

STEAM_COMPAT_DATA_PATH="/path/to/steam/steamapps/compatdata/20920" WINEPREFIX=$PWD 
    "$HOME/.steam/root/steamapps/common/Proton 5.0/proton" run ./drive_c/path/to/custom_application.exe