As I wrote before, I use iCloud Drive, and find it very useful.
I do not, however, use Documents and Desktop in iCloud.
For the regular iCloud Drive, documents that are stored locally in
~/Library/Mobile Documents/com~apple~CloudDocs/
- apparently, with the exception of those saved directly into application folders.
iCloud Drive has this strange duality: it shows "folders" named after applications (the ones that exist in both macOS and iOS, like Pages or Numbers), and also normal folders, which you may create using the Finder, and used to save any kind of document you want (much like in a normal folder in your hard drive).
Folders you create manually using the Finder are there, accessible even with internet, and in a known location.
Just try doing, in Terminal:
ls ~/Library/Mobile\ Documents/com~apple~CloudDocs/
or, in the Finder, press command-shift-G and paste
~/Library/Mobile Documents/com~apple~CloudDocs/
(note the subtlety: in the Terminal, you have to escape the space character between "Mobile" and "Documents", but you don't do it in the Finder go to folder window)
Guess what: Finder will take you to iCloud Drive.
Note: The folders automatically used by iOS applications are not accessible in Terminal, and understandably so - this would probably violate the walled garden philosophy of iOS, where you don't have real access to documents via the file system, and applications can only see their own documents (well, now a little more open using "Files" application on iOS)