Fresh install on an SSD made all the difference in world

Yes via symlink or change root game folder destination.

How to - msfs MS Store ver.

1 create new folder named MSFS 2020 on for e.g. D drive // D=external drive
2 copy Official and Community folders from
C:\Users\YourUsername\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages
and paste to D:\MSFS 2020
3 after that go to
C:\Users\YourUsername\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache
4 in notepad open file named userconfig.opt
scroll down to the bottom and edit last line
e.g.
InstalledPackagesPath "C:\Users\YourUsername\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages"

// Packages is root game folder
// D = external drive

change
InstalledPackagesPath "C:\Users\YourUsername\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages"

to for e.g.
InstalledPackagesPath "D:\MSFS 2020"

save changes

After that go to
C:\Users\YourUsername\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages\Official
delete all files and folders

Go to
C:\Users\YourUsername\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\LocalCache\Packages\Community
Delete all files and folders

How to - msfs Steam ver.

1 create new folder named MSFS 2020 on for e.g. D drive // D=external drive
2 copy root_game_folder Packages from
C:\Users\YourUsername\AppData\Roaming\Microsoft Flight Simulator
to D:\MSFS 2020
3 after that go to
C:\Users\YourUsername\AppData\Roaming\Microsoft Flight Simulator
4 in notepad open file named userconfig.opt
scroll down to the bottom and edit last line
e.g.
InstalledPackagesPath "C:\Users\YourUsername\AppData\Roaming\Microsoft Flight Simulator\Packages"

// Packages is root game folder
// D = external drive

change
InstalledPackagesPath "C:\Users\YourUsername\AppData\Roaming\Microsoft Flight Simulator\Packages"

to for e.g.
InstalledPackagesPath "D:\MSFS 2020\Packages"

save changes

After that go to
C:\Users\YourUsername\AppData\Roaming\Microsoft Flight\Packages\Official
delete all files and folders

Go to
C:\Users\YourUsername\AppData\Roaming\Microsoft Flight\Packages\Community
Delete all files and folders