The problems I saw: under Proton, I couldn’t even launch the game. The start button in the standard Matrix launcher thing launches a browser pointing to the Steam store page.
Under WINE, I can launch the game, but it gets confused about fullscreen vs. fullscreen with taskbar, and crashes when it tries to show the combat odds popup.
It’s a hard life being a Linux wargamer. Every developer has a custom engine, and none of them work quite right outside of real Windows.