This might be cheating but I'm assuming mods/DLCs to a game count as part of the game.
- Factorio. Pretty much endless amount of stuff you can do with mods on top of a top-tier base game.
- Minecraft, also for the mods.
- Geometry Dash. So many user created levels and the highest skill ceiling of pretty much any game.
- Asetto Corsa, or whatever the most realistic, moddable car racing sim there is. I don't play this game but I don't want that genre to die.
- ~~Really struggling to think of anything else so I'm just gonna go with another fun, replayable, moddable game: Balatro.~~ Edit: After reading other responses and me forgetting some games I think Skyrim would be a better choice here.