I don't think AC is ever going to work without some workarounds to get it to start. AFAIK the only one required right now for vanilla AC is protontricks 244210 dotnet472 corefonts and then I think it will start. GE might implement a fix for that I guess but honestly the vanilla game isn't worth playing without content manager at this point and that's a whole multi-step process to install inside the wine prefix and in the game root outside of steam, and not something GE can do anything about.

Anyway the process is much simpler than it used to be. Here's my notes from last time I did it about a month ago or so. I race (badly) in AC pretty much daily.

Install game
select GE-Proton8-25 (get it from github if you don't have it)
run game and let it crash (takes like 15 minutes)
protontricks 244210 dotnet472 corefonts (about 20 minutes)
add fonts from here https://files.acstuff.ru/shared/T0Zj/fonts.zip (readme)
Install Content Manager in .steam/root/steamapps/common/assettocorsa/
set launch options to c="%command%";sh -c "${c::-17}Content Manager Safe.exe'"
mkdir -p $HOME/.steam/root/steamapps/compatdata/244210/pfx/drive_c/Program\ Files\ \(x86\)/Steam/config
ln -s $HOME/.steam/root/config/loginusers.vdf $HOME/.steam/root/steamapps/compatdata/244210/pfx/drive_c/Program\ Files\ \(x86\)/Steam/config/loginusers.vdf
protontricks 244210 winecfg, then add library override for dwrite.dll (native, builtin)
Run game, will launch CM
echo 'Z:\home\'$USER'\.steam\root\steamapps\common\assettocorsa' then paste that in the AC location when prompted
install your key for the full version
install CSP, then upgrade to 0.2.2 (will say Can't find INIReader::cache when launching if you don't), then upgrade to the preview if you want.
install anything else you want like SoL, pure, etc.
Drive!