Simulators are one of the earliest PC game genres, and remain compelling experiences to this day, even if they're not as popular as they used to be.
I like all kinds of combat flight sims; the MS Combat Flight Simulator from 1998 was something special, and I've had some similar fun in IL-2 Sturmovik. The newest civil air sims are pretty great too, I'll pop on a podcast and make a flight. They're particularly cool in VR.
I've also found the MechWarrior games to be fun, but I've only played 2 and 5. I got to play a bit of Steel Battalion with the full crazy controller at a con a few years back, and that's got to be a lot of fun once you really know what you're doing.
So what's your favorite sim?
Train Sim World. Yes Dovetail have their problems, yes its expensive if you want a lot of the latest DLC (why, its not multiplayer so doesn't decrease in popularity like multiplayer game DLC), yes its not a well optimised graphical tour de force. But damn is it relaxing to play with multiple levels of difficulty that are entirely optional. Its possible to get hundreds of hours of replay from a single route if that's what you enjoy.
Pick up Derail Valley Simulator. It's not as pretty, or expensive, but good Lord is it satisfying to learn how to NOT blow up a steam engine.