It seems like there are dozens of places it could be depending on a whole bunch of factors and how it is installed. However, there is an easy way to find them. Flight simulator itself will help you do it.
Start msfs2020
After it loads, start developer mode as follows:
Go to options in the start up screen after msfs2020 loads. Then choose:
General
Developers
Then turn developer mode on
Then “apply and save” at the bottom
Then “go back” at the bottom
Now you will see some tiny letters above the main menu choices. Choose
Tools
Virtual File System
Then open the right arrow
Then Watched Bases
Hovering on the third item will show you where the community folder is. Just write down the file directory path.
Don’t forget to go back and turn off developer mode.
OK, after I posted the above, the system removed all my tabs and structure. Shoot. Hopefully you can follow it anyway. “open the right arrow” means to click on the arrow at the left of that line. Doing so will open the sub elements of that menu item. Hope this helps.
Cheers!