Mostly endless, quite possibly story-less games. Played this sort of stuff a lot more in the past, nowadays either when I'm too tired for anything else, or I'm on a playthrough.
Some cool endless games I can personally recommend include:
Deep Rock Galactic
Cataclysm: Dark Days Ahead (playthrough-friendly?)
Trackmania
Monster Hunter (playthrough-friendly, up to GenU)
Animal Crossing (playthrough-friendly, up to New Leaf)
ArmA 3
Left 4 Dead (2) (playthrough-friendly)
Counter-Strike (just don't open cases, and, if you're really bad with gamba, avoid the Armory as well)
(maybe in 5-10 years when it will be more complete) Helldivers 2 – will play Helldivers soon
Space Station 13
Club Penguin
Bloons TD 6
Stardew Valley (playthrough-friendly)
Foxhole (not for everyone, likely not even for me)