Most hours spent on one game?

Csgo somewhere around 6k hours

minecraft I spend a lot of time on mods

I think about 2000 in Garry's Mod. Probably more in other games it's just steam is the only one that records hours

I spend 1000+ hours on CS:GO. the secound on this list the Rainbow six:siege with 900+ hours.

How many times have I passed the witcher

GTA Online probably.
Over 30 days in game so about 900-1000 hours.

... across 8 years!

mine will be fivem with over 5,000 hours to date

not as much as many people I know but still quite a lot imo I think I spent like 183 hours on Kenshi

gta5 by so far. played around 600 hours

stardew valley with over 600 hours