I discovered today that my most played game on Steam is Astronner with about 500 hours, and my second most played is Surviving Mars with about 500 hours.
Minecraft. I don't know how many hours, but I bought it before nether portals were a thing and I've been playing it ever since. Sometimes a game just clicks for you.
What do you even have left to do in Minecraft at this point? Not asking to be rude, but as an ADHD guy I actually can't imagine playing a game that much!
I probably spent the most time in Red Dead Redemption 2 or ARK, but that's because I went for 100% completion and there were always things to do for me. Once I completed the games (about 400 hours each), I was over it.
Modpacks. There are hundreds. And probably tens of thousands of mods. You can easily make your own modpacks nowadays, using a launcher and config editor.
It's been so long since I've played the vanilla version, I haven't seen any content from the last few updates. I've started a vanilla world just to explore them.