On the top of the list is XCOM2 with 1100 hours. I usually don't spend more time on games than it takes to beat them. I'm not a fan of hunting for collectibles or achievements, so after finishing the campaign I'm usually done with them. Not with this one though.
Of course there are games where there is no keeping track of how much time I spent on. One honorary mention has to go to Transport Tycoon, which was released in 1995, and I still actively played it 20 years later. Haven't done so recently, but there is always a chance with that. I must have spent at least 1000 hours on it, neglecting studies in all levels of education.
The second game is BeamNG with 420 hours. Quite a feat for a completely aimless game, with no goals just mindless fun.
The third most time I've spent on is Train Simulator with 350 hours, but at least some of that was contributed by my late father as we used to share a steam library.