I do a lot of drag & dropping on my iPad and it’s currently not possible to drop onto folders, only long-holding until DT opens the folder, then releasing. Here’s a video:
Sorry for the weird crop, I didn’t want to show the thumbnails of what was in those items but you get the idea 
Other quirks related to groups: that sometimes mess with things: Selecting multiple items and hitting CMD-ALT-G sometimes opens the “Go To Page” dialog for whatever reason. And when going through the menu it creates a group with 1 item, even though the sidebar has multiple selected
(While I’m at it - a shortcut for “set name as” would be very lovely. File organization and quick name setting are my most common actions)