Game was working fine under GE proton, then borked. Wouldn't get past the splash screen. I tried verifying integrity of game files over and over with different proton versions to get the install script to work properly. In the end, using proton tricks, I ran the emulated uninstaller and removed everything except Wine Mono Windows Support from the prefix (there were multiple versions of Microsoft VC Redist for some reason). Verified integrity of game files again, switched to Proton 7.0-6 as suggested by others and the game now works flawlessly. Install scripts worked and EAC is functional.

It may work straight out of the box then break one day. I've never had this issue before so your mileage may vary.