The steam deck sometimes has trouble with external launchers.

Try these steps.

1. Hold your power button until you see a screen pop-up, click "switch to desktop."
2. Open steam in your desktop, launch crossout in your library as you would for pc.

It should just work like normal in desktop. I haven't tried my own deck with the game, so I don't know if controller support will work in desktop mode by default.

Same problem. Using Proton Experimental can help launch the game, but only for like 5-10 minutes, then it crashes.