Hi, had the same after reinstalling from DVD.
Although you do not use the Xbox app this might be the problem:
Log off form MS store
Log off from Xbox app
Uninstall the Xbox app
Download and install the Xbox app
Log in the Xbox app
Log in MS store
It is better described here:
https://flightsimulator.zendesk.com/hc/en-us/articles/360016892819-Access-to-the-content-servers-is-currently-unavailable-error-message
Good luck