I find Townscaper really relaxing, there’s no objective, just a toy to make cute looking towns. Haven’t tested it on steam deck tho.
If you like building/puzzles there’s Shapez (this one I tried on steam deck and it might take some time to get used to the controls), it’s like factorio but abstract and without resource management, you just make machines that modify and combine shapes to create new ones, it get’s progressively complicated, if it’s your thing you’ll find it quite addicting so be mindfull of that.
Both FAR games Lone Sails and Changing Tides: Puzzle platformer with a story told just with the environment, I recommend playing both one after the other in order
SteamWorld Heist: Tactical RPG in a side 2D perspective with ricochet. I haven’t played much of this one but it’s very cool
Gris: an interesting platformer with really nice looking animation
A Short Hike: A cute adventure game about exploration
Oxenfree: An interesting graphic adventure with a cool story
Night In The Woods: Platformer adventure with an interesting story and great characters