Steam Deck

Deep Rock Galactic, I play it exclusively on single player with the little robot buddy. On easier modes it’s pretty chill and pauses well if you need to stop in the middle of a mission.

Sable is just a relaxing exploration game. No real combat, just riding through a desert on a hover bike. Cool art style.

Inscryption is a creepy deck builder, with some wild turns. Don’t look up much or spoilers abound.

Moonring is a free old school rpg. Graphics are classic but the game is a great throwback with some modern gameplay.

Dave the Diver for sure

If casual means relaxed to you, factorio. Their new controller integration is great. But be careful, it's highly addictive.

I'd say Placid Plastic Duck Simulator, but that is a bit heavy for the Deck.

Sunshine Heavy Industries is "stick together legos to build cool looking ships".

Toem is a great little easter egg hunt with your camera.

Rain On Your Parade is a dreadfully cute "you are a cloud and you cause problems" campaign.

Unpacking, Hardspace and more are in a Humble bundle right now, heard good things about them

Peglin and Dome Keeper are pretty great.

Also Rogue Legacy 2 if that's your kind of thing.

I really enjoyed both Ori and the Blind Forest and Ori and the Will of the Wisps. Beautiful 2D platformer with great soundtrack. Find the bundle on Steam

Noita, Slay the Spire, Children of Morta, Brotato...

The Lego games! Perform well on the deck, are often on sales and cover many different franchises. The games aren't difficult, but there's plenty to do and explore and a good bit of humor. Currently playing through the Skywalker Saga, super easy to pick up and just explore

Binding of Isacc: Afterbirth+ feels like it was made for the deck.

That solely depends on the question what you consider "Casual". I'll go with the definition "a game that doesn't need a significant time investment per play-session".

• Super Hexagon: Amazing music, simple game, but challenging.
• Triptych: Tetris with soft body physics. The game is great, the sound a bit annoying. Also, I don't think it's available on Steam, so it needs manual installation (and input bindings).
• Cultist Simulator: While the game is very obscure, it doesn't require a lot of time per session - you can start it, play 5 minutes, and exit it again.
• Hades: It's a Roguelite. You die. A lot. That's why each session can be rather short.
• Loop Hero: It's not as "casual" as the others, as it takes some time for each run, but not too much.

Peglin was incredibly fun on the Steam Deck.

I've heard good things about Cozy Grove, though I haven't played it yet. Seems like a good Steam Deck game

I use the Heroic Games app to play my GoG and Epic Games library.

Turnip Boy Commits Tax Evasion was free last week so I’m playing that and it’s cute/fun.

I like to play roguelites, adventure games, and side scrollers when Im out. So I'd recommend Wizard of Legend, Lunistice, A Hat In Time, Dead Cells, Hollow Knight, Bomb Rush Cyberfunk, and Hi-Fi Rush.

All of these games are less than 20 Gb, and they're great on the deck. Hopefully they go on sale soon for you.

Risk of rain returns just dropped, that's going to have a permanent home on my deck's ssd

Lil Gator Game for a pretty short (maybe 4ish hours), VERY cute love letter to growing up and Zelda. 3D adventure sort of platformer I suppose, not dissimilar to A Short Hike

Goat Simulator is always fun

Wedding Witch

Having slot of fun with cocoon right now

ULTRAKILL, Halo MCC Multiplayer and Super Hexagon.