(This may have been posted already but here it is from me. )
Adding new scenery and aircraft is easy, provided you know where your Community folder is located.
Downloaded files are simply unzipped then drop the folder into your Community folder
Here is a quick description:
Default installations.
Microsoft Store version
C:\Users\USERNAME\AppData\Local\Packages\Microsoft.FlightSimulator_RANDOM\LocalCache\Packages\Community
Steam version
C:\Users\USERNAME\AppData\Roaming\Microsoft Flight Simulator\Packages\Community
If you installed MSFS in a location of your choice you may find it here
C:\Users\USERNAME\AppData\Roaming\Microsoft Flight Simulator\Packages\Community