when you have excluded the impossible, whatever remains, however improbable, must be the truth
Either it’s the device to which the UI belongs, the device you are editing or other devices. It talks about adding additional devices with mutually shared folders -> can’t be other devices. The setting is present on multiple editable devices -> can’t be the single device the UI belongs to.
Singular -> not other devices. Available on all devices -> not local device.
Ok, here Holmes might not be applicable, as you might not be able to come up with any possibilities. The true one is: If the advertised device already exists locally, it doesn’t need creating (well can’t be), just sharing it.
That doesn’t mean it couldn’t be easier to eliminate the impossible (or simply understand what it means), but without either explaining your thought process and where it fails to come to a conclusion that you feel confident on or proposing better wording, there’s nothing to be done.