Backup MSFS packages installation folder.
After installing windows10 - install MSFS launcher and point to the correct package installation folder.
Also backup folders named:
ACTIVITIES
c:\Users\YourUserName\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalState\MISSIONS\ACTIVITIES
WGS
c:\Users\YourUserName\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\SystemAppData\wgs
because if something went wrong you may lose: bush trips, controls settings.