When ADDING FOLDERS from an external drive WITHOUT MOVING, currently Mylio automatically makes this drive an additional vault.
My guess is that especially when working with large or very large libraries all have already set up minimum 2 dedicated vaults as strongly suggested by Mylio.
So one doesn’t need another vault, which automatically imports all photos from OTHER PLACES onto this drive. The space on such a drive is precious and should be used for a growing collection and not for an additional vault which I don’t need here. If for sync reasons Mylio needs a Mylio folder with a library backup and max thumbnails, that would not take up too much space - but please not more!
Thank you to the Mylio developer team!