Hohokum, it was a PS+ game on PS4 a few years back. It's great, superb soundtrack too.
Celeste maybe?
Also I find that Skyrim is a great chillout game. A nice open world and a game where you can have fun just exploring without doing any major quests. I also like GT Sport, I like driving games and just have a nice relaxing time driving cool cars around beautiful tracks whilst listening to a Youtube video or a podcast
This is my voteTetris Effect
I tried mantis burn racing on ps now trial and fund it quiet relaxing to play
Great game and underrated / not talked about much but I'm too competitive to find it relaxing!