For me it was Terraria, Satisfactory, Tetris Effect Master Mode, Minecraft with Mekanism mod & CSGO / CS2 (almost 2000 hours in CS alone).
Edit: There are so many answers that I might only reply if I have something interesting to say. I will read all of your answers though. 🙂
Edit 2: It has become too much for me and I have to disable notifications. Thank you for the massive response and please continue to discuss with everyone here. ❤️ 🫡
Crash bandicoot 3 was my first heperfocus game. I played that game until I finished all levels, first time I did that my entire life. Second one was Skyrim. I played it so much!! I clocked over a thousand hours on the vanilla game, and I played more modded than vanilla, I can’t tell how much I played in total because steam didn’t track my modded playthrough. Then there was super Mario Galaxy (I got every star except the stupid thrash bombing one and I’m still so fucking mad about it). My most recent ones are monster hunter world (plus DLC) and current is monster hunter wilds, I’ve already 100% it and am in the process of crafting every single armour and weapons
Monster Hunter World is a superb game!