I’m not an expert, but MSFS relies on Microsoft Azure, and Azure uses PlayFab as a backend management of gaming services. I’m not sure what aspects of MSFS use Playfab (if any), likely some of the initial authentication, and also any of the multiplayer aspects. Microsoft and the Forum managers here have mentioned it before.
The reported Playfab issue is a minor issue ongoing for several days, see the logs below the graphs.
We have no other reports of any connection issues at this time.
These reports are available in the top pegged article in the very first category of the forum.
Here is a link to this article which is in the Official Microsoft Flight Simulator / News & Announcements category: