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 without question. CS along with some rts games like zero hour and CoH used to be up there but it's not even close. Got to a ranked immortal at my peak. Still, was a lot of fun playing with friends and family, so not like it was always a solo activity. Glad I quit though.