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. ❤️ 🫡
DOTA 2, man. Once you get past the massive learning curve, there is just so much to do in-game. Every match is entirely unique, with constant updates, tournaments, battle passes, and what have you. When I feel like disappearing, I disappear into DOTA.