For the longest time, I searched for the "one game". The game that would become my forever home within the gaming sphere, always pinning my hopes on mostly story-less, endless experiences. And while I've loved them, and still enjoy a game like that from time to time, nowadays I'm leaning more and more towards that home being hidden in a combination of other things and hobbies, not a single title.
Some cool endless games I can personally recommend:
Deep Rock Galactic
Cataclysm: Dark Days Ahead
Trackmania (only played the 2020 version)
Death Stranding (delivering cargo)
Monster Hunter (only played 4U)
ArmA 3
Portal 2 (custom maps and games)
Left 4 Dead (2) (replaying, custom maps and campaigns)
Team Fortress 2 Classic
Spelunky (yet to play the sequel)
(maybe in 5-10 years when it will be more complete) Helldivers 2