I’m assuming this is docked? You’re playing a game docked with a Steam Controller, put it in sleep, come back and you can’t do anything in a game but can get to the main Steam Menus, etc? So here’s you fix this issue. When you’re done playing, you have to go to the Settings, Controller settings and re arrange/put the internal Steam Deck Controller as controller 1 and the Steam Controller/Bluetooth controller as 2. On wake up turn the deck on then turn the Bluetooth controller on and swap it back to 1.

This is assuming you’re having an issue on wake up from docked after putting a game to sleep.