OK. Makes sense. 
The problem you are having, others have the same where the MS Store does not recognize MSFS. All other apps from the Store will work. This has been an ongoing problem. All the other troubleshooting steps that we have not tried… will also fail to work. I’ve seen it too many times. 
The only thing that makes it work (about 50%) of the time is when the next update gets pushed out. Others have solved it by creating a new user account on the PC (but we shouldn’t have to do this).
Let me research some past posts.