I was disappointed that the X internally renders games at 4K regardless. I would have much preferred to play FPS games at a lower resolution for higher framerates but that wasn’t how it worked for any of the games I tried (Crackdown, Far Cry, a couple others).
That’s actually offered for a number of XBox One X enhanced games:
This is a List of Xbox One X Enhanced games. Games here are enhanced by console specific updates/patches when played on an Xbox One X.
Xbox One games without an Xbox One X update/patch, including Xbox 360 and Original Xbox backwards compatible titles can also take advantage of the Xbox One X's hardware. These improvements can include the following:
There are currently 220 games on this list.
Notable examples: The Witcher 3, Forza Horizon 4, Rise of the Tomb Raider, …
That said, The Witcher 3 originally couldn’t quite hit the 60fps target:
(I think there were patches afterwards, but not sure whether they ever hit a stable framerate)
That mode is superb on FH4 though:
Overall, you get enhanced visuals and more stable framerates on pretty much all games. But some games offer that 60fps option.