WARNING!!!! WARNING!!!! WARNING!!!!!
iCloud Drive is completely broken in current Catalina Developer Beta. If you install Catalina in your Mac, you won't be able to have not only Desktop and Documents in iCloud Drive but
ALL of your iCloud files and any application related to iCloud files like Books.
You will see the files but couldn't open them.
On iOS 13 iCloud Drive is buggy as well but most of the programa should work fine (but not Books, for example).