Adapted from this guide, to be more accurate for (my) Arch Linux
Install AC from Steam
Force Proton compatibility version to 5.0-10 (right click Assetto Corsa
in Steam library, select Properties..
) and try to run the game - it will prompt you to install .NET 4.5.2, accept it. It will crash after that, that is to be expected.
Run the wine configuration tool using that same version of Proton on the game's wine prefix:
WINEPREFIX=/home/$USER/.steam/steam/steamapps/compatdata/244210/pfx WINE=/home/user/.steam/steam/steamapps/common/Proton\ 5.0/dist/bin/wine winecfg