So, you need to switch to the "Linux Native" branch, same place you switch to "beta" servers or whatever in properties of the game in steam prior to launching. Now, I ran into the same issues many reported previously of not having the executable game file anywhere. However, what ended up fixing this some how was I installed the "Proton Hotfix" branch of Proton, let it install and fail working, then switched back to "Linux Native" no proton or compatability and it just works. It works greats. I'd love to get a new server going we need more linux native people playing.