So I see this is a long-standing unresolved bug. That’s concerning, as a paid subscriber, as moving folders seems to be a fundamental feature of any editor. But I digress.
The solution I’ve found to overcome this bug is to create a blank page at the bottom of the page list. This then allows me to drag folders above that blank page and reorder as I see fit.
It does mean that to reorder folders I have to drag every single one, but that’s a heck of a lot easier than the official workaround detailed here: Moving Folders in Pages Panel