desktop and documents on both icloud and mac

If you enable iCloud Drive in System Preferences > Apple ID > iCloud, then click "Options" and enable "Desktop&Documents", the Desktop folder and Documents folder sync between your Mac and iCloud.

Disable the checkmark "Optimise Mac Storage", if you want keep all items stored locally and not removed from the Mac to save storage.

Your Desktop and Documents folder will be removed from your Home folder but still be mirrored on your Mac and backed up by Time Machine, and you will be seeing it in the iCloud section of the Finder sidebar.