Thank you Richard.Taylor for your helpful explanation. Following instructions in Apple Help to the letter, I have not been able to move or copy files/folders in "iCloud Drive" on icloud.com back to my macbook pro by dragging-dropping or copy-pasting. Nothing happens and the selected files just sit there, unresponsive. Maddening.
But your explanation pointed me to the (not) missing files and subfolders on my hard drive -- as Not revealed by Apple Help (in my searches). It was then easy to drag-move them back to the recreated Documents and Desktop folders (as Apple Help does describe).
Like other lower level mac users here, I've found the latest Apple Help instructions not only incomplete but specifically incorrect/obsolete. Richard.Taylor Is better informed than many -- including the most recent Apple Help writers. Good! This is the point of the community, no? Thank you from one of the misinformed masses.