Elden Ring closes instantly when I hit Play

Elden Ring just closes the moment I hit Play in Steam. No error, no window, nothing. Other games I have tried work fine. Fresh GlouOS install. Any ideas?

Steam Play probably is not on for it. Steam > Settings > Compatibility > tick 'Enable Steam Play for all other titles', restart Steam, then try again. If it still sulks, right click the game > Properties > Compatibility and force a Proton-GE build.

Wiki has the walkthrough: Steam and Proton

That was it Steam Play was off