Retested today with the latest Proton Experimental, issue persists. For what its worth, it would be perfect game for the SteamDeck ^_^.
Don't exactly have the game on hand to check, but I am seeing reports on protondb mentioning that using protontricks to install dxvk fixes the menu on deck. Dunno why it wouldn't work with protons DXVK though.
proton experimentalx2 2022-02
Compatibility Report
System Information
I confirm:
steam-102810.log
Symptoms
The menus and HUD (scaleform) is not rendered at all.
Reproduction
A 100% reproduction rate, just launch the game. When the music starts and the (in-engine) background is being rendered with planes and soldiers there is nothing to select. Input does work.