Here are the paths of my Steam-MSFS2020:
You have the default steam installation path or modified? -> modified: "D:\Steam\Steamapps\Common\MicrosoftFlightSimulator"
There is a file "C:\Users\USER\AppData\Roaming\Microsoft Flight Simulator\UserCfg.opt"? If not: Where is it? -> It´s there
What is "InstalledPackagesPath" (last line) in above file? -> "D:\Steam\steamapps\common\MicrosoftFlightSimulator"
Full path to base files (containing folders "fs-base" and "fs-base-nav") is "C:\Users\USER\AppData\Roaming\Microsoft Flight Simulator\Packages\Official\Steam"? -> "D:\Steam\steamapps\common\MicrosoftFlightSimulator\Official\Steam"
Full path to community is "C:\Users\USER\AppData\Roaming\Microsoft Flight Simulator\Packages\Community"? -> "D:\Steam\steamapps\common\MicrosoftFlightSimulator\Community"
