The Community folder in MSFS is where addons purchased or downloaded outside the in game Marketplace are placed to load in the sim.
The community folder is located in "%LocalAppData%\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages\Community"
To find the community folder simply:
Open file explorer
Click the top bar (shown in below picture)
Paste the following path: %LocalAppData%\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages\Community
To install addons in the community folder, do the following
Download the package
Unzip the package
Look into the folders until you find the manual
At the same level of the manual will be the folder that goes into the community folder
Move this package folder that you just identified into the community folder
Making sure you're not one folder too deep
It's easy to end up copying the folder containing the package that belongs in the community folder into the community folder instead. Ie copying KBLU - Package into Community rather than "xcodr-airport-kblu-blue-canyon".
If your scenery isn't showing, it's a good starting point to check. If the folder name isn't <developer>-airport-<icao>-<name>, all lowercase, no spaces, then you most likely copied the folder that contains the correct folder, rather than the correct folder.
To resolve this situation, simply look into the folder, and keep opening folders until you find the one that matches the above naming convention. Then, move that folder back into the community folder, and delete the folder that you're in which is now empty.