I had alot of issues making this work - my problem seemingly was the launcher either not showing on proton versions lower than 9 or just flat out freezing after launching on 9 and onward

Found out there has been a documented issue of playing the newer versions of the game after 1.10.2 (https://forum.paradoxplaza.com/forum/threads/known-issues-1-11-1.1612687/)

I found this suggestion on the paradox forums (https://admin-forum.paradoxplaza.com/forum/threads/game-doesnt-start-linux.1702216/)

Which led med to installing the steam client directly from steam rather than flatpack/PopOs! - that made everything work and it fired without issues the first time after installing

Milage may vary - best of luck <3