One of my main reasons for going with the XSX over PS5 at the start of the gen is having BC with all three of MS other generations, among other things.
Not complete BC though but I guess you are aware of that?
XSX has BC with:
All XB1 games (except Kinect games)
~25% of Xbox 360 games
41 original Xbox games
Still better than PS5 BC but far from complete.