I don't think this is legit, as it seems like a step backwards in terms of the direction of the Xbox One dashboard. They just got rid of the "tabs" at the top, so why would they just add them back in for Xbox Series X? Also, I hate how UI designers (including people making fakes for leaks) seem to think it's okay to waste a bunch of space. I think Microsoft got things a little more correct with the preview dashboard layout, but I still want more of my recent games/apps to show up on the first screen I see when I boot up my Xbox One X. How hard is it to not leave a bunch of empty, wasted space on the dashboard?
Assuming this isn't just a Photoshopped mock-up, I'm gonna say that this is a Kodi skin or something.