Update to say: dragging files from an external disk worked for a couple days and then stopped and is now working again. However, the cursor never changes to an alias arrow.
I should add that I use 12 separate desktops (from which Jony Ive decided to take away the ability to differentiate from one another by their Wallpapers or open documents while also not allowing the user to rename them appropriately--one of his many "accomplishments") so this also involves swinging from one desktop to another. That's been occasionally temperamental for years. It just feels and looks different now.
At this point I don't think this is a DVDPedia issue, now that I've played around in Mojave land for a couple weeks. Ugh
