Many thanks Michael,
for your quick and detailed answer.
But the android app Foldersync cannot have a PC local drive as a destination, but only: 1) an Android local folder 2) a cloud account like Gdrive, One Drive, etc
So the point 5 of your list cannot be done by FolderSync.
But this post:
https://github.com/cryptomator/cryptomator-android/issues/4#issuecomment-287795036
doesn’t mean that Cryptomator can now encrypt local Android locations ?