Unfortunately I have been using Bazzite so long I’m not sure exactly how to explain how to do it on SteamOS, but…

So your Deck, when Steam is still running, is also running the layer that translates your joy and buttons and track pads and what not, as managed via Steam’s controller profile system.

You can go into steam and find a button for something like a default desktop config.

You can uh, tinker with that profile and make it so a hot key or combo switches it over to just acting as basically an xbox369 controller.

When you are in that mode, Lutris, emulators run in desktop mode, etc… they should recognize your joy/trigger/button inputs as if they were a 360 controller now.

It… can be a bit confusing, but its not impossible to set up, at least not with the emulators Inhabe futzed about with.