If you want to know if a game works on the deck or not steam lists steam deck verification for games that work. If it’s listed as verified it’ll be a smooth experience, like launching a console game. If it’s marked playable it will have more detailed information about the game’s issues, most common is needing to use an onscreen keyboard for certain things or other UI weirdness.

Games that aren’t verified might work but you’ll likely need to tweak settings to get them running smoothly.