ARK: Survival Vvolved: 1919 hrs or 79 Days.
Fallout 4: 1396 hours or 58 days.
I would say I'm a fairly committed gamer - I build PCs, I have many consoles, I spent over a decade working on games magazines - but I'm sure I have never approached those stats. Of the 150-odd games in my Steam library, my most played is Metal Gear Solid V with 98.9 hours.
Next best/worst is Arma 3 (72 hours), then Civ 5 (51 hours), then Just Cause 3 (43 hours).
Edit: I missed Fallout 4! I played 82 hours of that on Steam, and it had grossly outstayed its welcome at least 20 hours before the actual end.
I've since transitioned over to Xbox which doesn't show my metrics AFAIK
Most games from Xbox One onwards keep your stats, unless the developer opted out (stats are shown in your achievement list / profile).
My profile shows MS Flight Simulator at 325 hours, although only about 130 hours spent flying (lots of time on the menu screens?) and Hitman 2 at 212 hours. If I add together Hitman 1,2 and 3 I get to 418 hours, but, you know, that's three massive games.
I have over 100K achievement points though, how about that?