turn off desktop for iCloud but keep documents

The Desktop and Documents option of iCloud Drive cannot be separated.

One option would be to turn off the Desktop and Documents option but leave iCloud Drive turned on and then put the folders that you do want to sync into the iCloud Drive folder in Finder.

See the following for information about Desktop and Documents: Add your Desktop and Documents files to iCloud Drive - Apple Support

If turning off Desktop and Documents, see the following from Add your Desktop and Documents files to iCloud Drive - Apple Support

Turn off Desktop and Documents

1. From your Mac, choose Apple menu  > System Settings. In macOS Monterey or earlier, choose Apple menu  > System Preferences. 
2. Click Apple ID, then click iCloud.
3. Under Apps Using iCloud, click iCloud Drive. 
4. Turn off Desktop & Documents Folders.
5. Click Done.

What happens when you turn off Desktop and Documents

When you turn off Desktop & Documents Folders, your files stay in iCloud Drive and a new Desktop and Documents folder is created on your Mac in the home folder. You can move files from iCloud Drive to your Mac as you need them, or select all of your files and drag them to the place you want to keep them.