Y'all- Nearly a year after this question was posed, I seem to have *SORT OF* figured out a work around for this.
Now, by no means is it perfect, and I guarantee it may cause some havoc for some, as the clarity of which sub-folder you're dropping into isn't the best, BUT:
What I've figured out is that if you CTRL+ Left Click on the folder you WANT to move (let's call this one "Receipts") you can then easily drag it into any of your other folders - be they primary folders (Inbox, CEO Office, CFO Office, IT, Etc) or sub folders (in this example, moving "Receipts" into the subfolder "Invoices", which might be a subfolder of "Finance").
It's not always foolproof though- What I'm finding is that sometimes in moving one subfolder into another more primary (or main) folder, others accidentally become sub-folders. This forces me to temporarily move them out, then back in- so a little time consuming, but this is the best thing I've found that works thus far.
I should note too, that there is a "move" option when you click the three dots next to each folder (under the same function as if you were to rename the folder)- but I haven't found that to be useful or functional at all.
Hope this helps someone. Hope this makes sense!