Off the top of my head, with recent games....
CP2077 with the ray tracing and all the extras turned on.
Elden Ring with the same. I think ER may still have some optimization issues but cranking everything up on it should test the system pretty well.
Dark Tide is also about to drop and I think it's pretty demanding when everything is cranked up.
Weird how my brain still thinks Crysis when people ask for a demanding game, even though it's old as balls now. I feel like "this game will melt your PC" isn't as much of a selling point as it used to be once graphics cards became so damn expensive.
crysis honestly holds up. the foliage / tree destruction and open world level design (ignoring the awful space levels at the end) promote interesting gameplay.
RE: op's question. . . Horizon Zero Dawn is really nice stylistically, imo. great environments if you ignore the robot dinosaurs trying to eat you. I guess it's an FPS though.
total war warhammer games can really bog down when you run at max unit size. turning off the U.I. and enjoying the carnage is great. the best way to play is mortal empires / immortal empires, but that can be costly to pick up all the factions. honestly a rip off, but if you have the $$$
dyson sphere program is pretty popular if u like factorio in space.
beamng can be graphics'd to hell and back, if you want, and the driving scenarios are finally updated and pretty fun. nothing like driving random italian backcountry roads until you die in catastrophic and highly-avoidable cliff dives
seconding No Mans Sky, though it is kind of a disappointment in terms of RNG. I have been wow-ed by many planets, like no joke some of the most interesting experiences I have had in recent gaming memory, but the majority of gameplay is kind of samey. I was trying permadeath NMS runs for a bit but the process of climbing the tech tree is genuinely boring.
finally, you might venture into VR games since, well, you have the kit to run them