@Mahares: i don't know how much they pay you for doing this, but you deserve a raise.
After 48 hours of struggle , i am again able to create a path to what used to be called "file.dirRootExternal". (on the tablet, not the SD or USB, ...)
Earlier, I was shown the right path with these runTimePermissions, but i would never have found this syntax.
Of course, your solution with the starter service causes me to rethink certain aspects,
but it seems to be more elegant than what i had before.
Thanks,
Paul