iCloud and Macbook backup other than 'Documents' folder?

You could put that folder in the iCloud Drive folder and it will sync (no need to turn on the Desktop & Documents option or to put it into the Documents folder).

Also, be aware that Apple offers iCloud Backup for iPhones and iPads but not for Mac computers.

It is possible to sync data from a Mac to iCloud if you turn on those options (e.g., iCloud Photos, iCloud Drive including the Desktop & Documents option). Syncing has some of the benefits of a backup (and the benefit of being offsite) but is not the same as a backup. Major differences include the fact that not everything on your Mac can be synced and the fact that if you delete something, accidentally or otherwise, there is only a limited time period (30 days in most cases) during which it can be recovered.

Also see:

Access and manage your files in iCloud Drive - Apple Support

and

Add your Desktop and Documents files to iCloud Drive - Apple Support

There is always a local copy if you don't turn on the "Optimize Mac Storage" option in Apple menu > System Settings > [username] > iCloud

(or on pre-Ventura systems, Apple menu > System Preferences > Apple ID > iCloud).

If you do turn the Optimize Mac Storage option on, there may or may not be a local copy depending on the free space on your Mac.