Can't drag and drop from Music app
This is a question and a FIX for drag and drop in the new Music app. This works to non-Apple devices, such as Sony Walkmans, or other external drive media players.
This feature is apparently removed from Music, despite existing in every preceding version of iTunes. Drag and drop is a fundamental feature of the Apple OSs, going back to 1984 - and despite any fathomable logic to remove this basic function.
I have been confirmed by Apple support that drag and drop has been (dragged and) dropped from Music. Apparently this is to make it better. It obviously does not make it better, but hinders the functionality.
So, some of the forum threads have a workaround for Apple devices (and you can actually drag and drop, despite what I've been told by Apple support - this kind of contradiction is not uncommon).
So…
You can't drag and drop to an external drive media player window, but you CAN select the tracks and use copy and paste.
It only took three hours on Apple live chat before I figured this out myself :-) I hope this helps someone with extraordinarily frustrating oversight in that app.