I have the GOG version of the game (+ Phantom Liberty DLC and some mods) but I run it on Steam with Proton GE 9.

○ The launch options I use also fix a problem with RED4ext, if you play without mods I think there won't be problems using same launch options as mine.

○ Also the game often freezes on wayland but runs fine on x11.

○ Excluding the things I already mentioned the game runs well with even a slight performance increase compared to windows.

○ If you have a gpu with little vram like my 8GB rtx 3070ti, particularly if you play in 1440p or more, and after few hours of gameplay the performace degrades a lot, it's a memory leak problem of the game; the only fix is to restart the game when it occurs.