Buying Series X, if I have Boarderland 3 physical disc is that going to work on Series X...

Yes, that will work on a Series X.

Any game that works on a Series X will work on a Series S and vice versa. Anything that is only listed as just Series X is usually the physical disc version since the Series S is only digital.

Yes, Xbox One game discs should work on the Xbox Series X consoles, as they are backwards compatible. So if you buy the physical copy of Hogwarts Legacy on the Xbox One, you should be able to play it on the Xbox Series X consoles, However If you don't have a Digital Copy or Disk Reader technology that reads disks and install them on you're Console it'll will not work on Series S as it's all Digital.

see i had bought the lego hobbit video-game on disc last week but when i asked at the cash desk of where i was going to buy it i asked if the game would work on xbox series x and i was told no so i never got it in the end so the disc version of lego the hobbit will work on xbox series x correct ?

Thanks for you support, and yes I have the Xbox series x and now I go to buy the disc ❤️