follow this with slight adjustments: https://www.youtube.com/watch?v=8qy_RQr8LbM

1. after you've launched a game once to make a prefix, placed content manager, symlinked loginusers.vdf, did protontricks -> winecfg -> libraries -> add -> dwrite
2. protontricks install from exe real .NET 4.5.2 as suggested by deiphiz, there's no need for installing anything else from protontricks.
3. launching the game takes a while, and it still spit errors about dwrite despite previous steps
4. launch the game again, as there should be no more errors
5. follow the video further
6. disable hardware acceleration and transparency in content manager settings because of black bars
7. after messing with settings, possibly due to unhidable "switch to orginal launcher" from CE settings, assetto corsa have deleted the AssettoCorsa.exe and wouldn't launch, symlinking again or making it read-only didn't help, just run: protontricks -> run exe -> AssettoCorsa.update.exe, it'll replace content manager as "AssettoCorsa.exe" on it's own.
8. in-game from right taskbar, paintshop disabled my LMB and had to disable "MMB switches to mouse steering" from CE settings, then MMB the paintshop icon from taskbar to disable it, then restart the game.