I have had exactly the same problem since the new release. I tried various ways to overcome the update problem but always ended up in an unsuccessful loop! In frustration, I had a 90 minute online chat and phone-call with MS (including screen sharing so that they could see what was going on) but even they couldn't solve it!
Subsequently I receved an email from the agent suggesting making changes:
Please can you try this procedures
Rename the Directory where MSFS is installed ( it's C:\Users\%USERNAME%\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe),
then click Uninstall in the xBox App,
Change the install Dir back to original name,
then click Install in the xBox App.
Took just over 2 minutes from start to finish and I now have 1.18.14.0 installed
Tried this and, guess what, IT DIDN'T WORK!!
I've given up on this until MS Store and XBox talk to eahc other to resolve what's going on.
As a customer, why should I be the one to resolve their own problems VERY POOR CUSTOMER SERVICE!