I believe they have worked out how to allow approved 3rd-party developers do testing on actual Xboxes by having a special flag on their Xbox account, which would allow them to upload packages to Marketplace that only they and any other specified flagged accounts could see and access for testing.
So that way, they can upload their alpha test packages via marketplace, and see them in their own accounts, install in the standard way on Xbox to test - but nobody else sees them.
My suspicion is that either Asobo or the Microsoft team are doing some additional ‘finalization’ code work after beta testing, as part of the final release, and for whatever reason, each time it results in an unintended and unforseen problem that happens to be game-stopping. If the code is changed, the version number should change accordingly, but it doesn’t. So it’s not adding up.
I’m sure hoping they are aware of this and working to ensure the pattern does not repeat, becuase it is increasingly frustrating to be unable to use MSFS as intended after this much time and testing.