Game installs on a separate mounted disk volume every time you start it. When you bought MSFS via Store there is no issue, it seems. But the volume can have a key that could be related to your game pass. They invented that as a kind of copy protection, @Bishop398 pinpointed it,
https://forums.flightsimulator.com/t/we-need-a-way-to-access-the-msfs-files-and-folders/179951/25
… so get yourself a legal version, update your game pass, checkin your new device somewhere… or call Microsoft game pass support line ? guess ? btw there are a lot of disks on the screenshot in that earlier thread… maybe free a disk position and problem is fixed ?