Supraland is the game you want - it fits all your criteria except the most important one: it’s currently Unsupported on SteamDeck. I found reports of people getting it to work but not without some fiddling. It has a sequel, though, which is just as good and which is Verified. The sequel is called Supraland: Six Inches Under.

The first game is an indie gem made mostly by one guy but it is very polished. This sequel was made by a small team. Don’t let the cute graphics throw you - it’s not a kids game. It’s a first-person open world metroidvania (not really a shooter, though there are enemies you’ll be hitting) with gameplay reminiscent of Portal, Zelda, and Metroid. Currently on sale for 40% off ($11.99). About 8-20 hours long.

It seems really dumb to play on such a device, but I've been playing a few rounds of Bejeweled 3 when looking for something in short bursts. There's a controller profile that works surprisingly well with the dpad + face buttons.

For laid back / cozy games, I recommend A Short Hike, TOEM, the Frog Detective trilogy & Dave the Diver.

Definitely check out INFRA (https://store.steampowered.com/app/251110/INFRA/) if you're into exploration puzzle games. I absolutely love the atmosphere in this game. It's on sale right now!

Control is great. It's beautiful and atmospheric and tells a great story, but shakes that up with some pure chaos and stuff flying everywhere.

Games that I've played recently on the steam deck:

Stray

Journey

Stardew Valley

Nobody saves the world

Guacamelee 2

Spider man Miles Morales

Road 96

Horizon Zero Dawn

Outer wilds

Raft

Rimworld

Football manager 2023

Uncharted legacy of thieves collection

Voltaire the vegan vampire

What remains of Edith finch

I kind of put the first few at the top because I think they might fit your request.

Portal reloaded and Tony hawk pro skater 3(ps2 emulator) are super chill games I can pickup and put down any time.