The important thing is that you MUST parse the UserCfg.opt, because that will contain the path the user selected when installing the sim, and that can be anywhere.
1- The UserCfg.opt file is always located in one of these folders:
MS Store version:
%LOCALAPPDATA%\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
Steam version:
%APPDATA%\Microsoft Flight Simulator
2- Read the UserCfg.opt file and parse it until you find a line containing this:
InstalledPackagesPath
The line contains this string followed by a space and then the path of the installed packages, which contains the Community folder, which is enclosed in double quotes.