Backward-compatible Xbox 360 games will still be available for purchase on the Xbox One and Xbox Series X|S stores, Microsoft says.
So no, presumably Microsoft just doesn't want to deal with the tangle of close to 20-year-old code that holds up the Xbox 360's store interfaces.
With uMatrix enabled: 99%, everything except ads-api.twitter.com and ads.youtube.com was blocked.
With uMatrix disabled: 83%, 125/150 blocked.