a hint about that… this game is NOT a usualy Steam game. You install with Steam only the main-app and all the content is managed then by MSFS itself ( also not the MS-Store, it goes again further on to a Asobo whater server/account thing ).
Have you tried ?
How is your setting for that ?
And we still wait for informations about:
You sould stop these network-cutting. Nobody knows exactly whats happens in such cases 
We have one case in forum, where seemingly a game-setting cause the CTD, which is of-course also stored within your steam-cloud.
If you realy sure that the issue comes not from login, xbox connection, virt. memory, AV-protection, etc., you can try to remove all your settings.
But be aware that you possible lost logbook, etc. …
EDIT: corrected link