But the GoG version? It’s rated Platinum in winehq…

Played out of the box for me in steam(with proton enable) last night for me.

I did have problems with my mouse not going all the way to the right wide of the screen in Wayland though.

I played over two hundred hours of the steam version on Proton 8

Unless something has changed, it plays fine through Steam with proton.

ProtonDB confirms: https://www.protondb.com/app/233860

I had no problems at all as recently as this year. I think I was playing over the summer