https://wccftech.com/xbox-series-x-higher-resolution-ui-4k-testing/

The Xbox Series X is an impressive piece of hardware, but it shipped with a rather odd limitation – the system’s UI is limited to only 1080p (the PS5 on the other hand, runs at a full 4K on appropriate screens). This was likely partly done in name of consistency, as the Xbox One and Xbox Series X/S share the same UI, or perhaps Microsoft was just worried about performance. Either way, the XSX’s menus definitely aren’t quite as crispy as they could be.

Well, it seems that’s about the change soon, as the latest update for those in the Xbox Insider Alpha ring includes “increased resolution” UI for those playing Xbox Series X on a 4K screen. It seems this feature won’t be available for Xbox Series S. Note, Microsoft isn’t actually promising full 4K – in all likeliness, they’ll be offering variable resolution in order to maintain performance. That said, I’m guessing it will be pretty close to 4K, unless the Xbox UI is way less efficient than we thought.