The game worked perfectly on proton hotfix and experemintal in skirmish and online mode; however, the campaign mode was always getting stuck on the loading screen.

so I had to switch to proton GE9.0-4 and after to switching that everything worked flawlessly.

Everything will work flawlessly with any proton version accept for the campaign mode. if your campaign mode gets stuck at loading screen just switch to this proton version 'GE-Proton9.0-4' proton version and all issues will be solved without any problems.