Hi There,
I had the same issue actually. Really frustrated that I could not "copy and paste" or duplicate a render layer easily.

I think I've found the solution:
Instead of copy and pasting - Right click on your collection and "export selected" - saving the collection as a .json. Then, when you want to add that collection to another layer, right click that new layer and select "import user template".

Edit: Just realized there is a limitation to this however. If you change the collection in one layer it wont update in the others. Though I guess they would tell you to use some sort of expression to populate the layers instead... *shrug*

I don't understand why they wont let you alt/ctrl + drag collections. It's ridiculous. If anyone out there knows a better way, please let us know.
-J