Unity Ver: 2019.4.8f1
Is this how Unity has always handled duplication of assets or is this a bug I’m looking at:
Duplicate option in edit menu?
Nope doesn’t work.
Duplicate option in right-click context menu?
What option?
CTRL+D, which is the shortcut for the not working duplicate option?
Oh yeah! That’s it!

Dug into this a bit more, it happens with undocked / floating panels.
So, I had my project panel moved across to a second monitor. As soon as this happens selecting ‘duplicate’ from the edit menu won’t work even if an asset is selected and highlighted.
I’m finding myself wanting to use the editor more and more over two monitors. I’d love to see Unity better work with that.