I upgraded to a high end PC in the Fall, mainly for MSFS2020, but as mentioned, RDR2, Control, recent AC games look impressive, and Witcher 3 maxed out is pretty glorious. GTA5 definitely looks really good maxed, too.
Edit: almost forgot Tom Chick’s GoTY, Cyberpunk 2077, which looks incredible.
Serious answer, one of the first games I tried on my new system last year was Total War: Warhammer 2 to enjoy the beauty of maxxed out settings and everything running nearly buttery smooth on my 34 inch monitor. I think the first game I tried though was Dominions 5, but that was only because an MP game was underway at the time.
Games I’ve yet to try due to time constraints:
Skyrim SE (heavily modded)
Any of the recent Doom games.
Planet Coaster.
I was very impressed by Hitman 3 and Doom 2016 on my 3060 Ti. Also played RDR2, Ashes of the Singularity and Anno 1800 maxed out. None of these shows off RT or DLSS yet, but I am looking forward to that eventually. I held off on Cyberpunk (which was going to be my first RTX game) due to the bugs.
Remember that gamepass is not available to most of the world. At least not legitimately.
Anyway, I second “any latwst Ubisoft game”. My personal preference is Odyssey but if vikinga or mummies are you thing they got you covered too. Watch Dogs Legion has a nice looking city. Red Dead Redemption is probably the nost realisticly looking game but the world is relatively boring, it’s just cowbow countryside.