First make a clean prefix for Steam Proton (this is necessary to get .NET Framework to work):

WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ wineboot --init

Uninstall Wine Mono Runtime:

WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ wine uninstaller

Install .NET 4.0:

wget 'http://download.microsoft.com/download/9/5/A/95A9616B-7A37-4AF6-BC36-D6EA96C8DAAE/dotNetFx40_Full_x86_x64.exe'
WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ winetricks winxp
WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ wine dotNetFx40_Full_x86_x64.exe /q && WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ wineserver -k

Change the prefix to Win 7 and set mscoree to native from winecfg:

WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ winecfg

Install .NET 4.72:

wget 'https://download.microsoft.com/download/6/E/4/6E48E8AB-DC00-419E-9704-06DD46E5F81D/NDP472-KB4054530-x86-x64-AllOS-ENU.exe'
WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ wine NDP472-KB4054530-x86-x64-AllOS-ENU.exe /q && WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ wineserver -k

​

If you want to use original launcher you must set prefix to Windows Vista:

WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ winetricks vista

Now just install/launch the game from Steam using Proton and it should work.

--

If you want to use Content Manager you should also install Visual C++ Redistributable 2015:

WINEPREFIX=~/.local/share/Steam/steamapps/compatdata/244210/pfx/ winetricks vcrun2015

Additionally to get Content Manager work in Steam I had to add "Content Manager.exe" from "add a non-steam game..." and force it to use Proton. Then I had to go into "compatdata" folder and replace the prefix that Steam made to it (mine was 2147483650) with a link to Assetto Corsa's prefix (~/.local/share/Steam/steamapps/compatdata/244210).

Renaming "Content Manager.exe" to "Content Manager Safe.exe" might help if there is any trouble to get it running.