May you elaborate? What does it offer more? Since Nextcloud and Duple do offer backup as well.

Nextcloud is a web app that lets you work with files and offers lots of other plugins too, like e-mail, calendaring, office, contacts. It's not a backup program. See https://nextcloud.com/ or https://en.wikipedia.org/wiki/Nextcloud

You might, for example, use restic or borg to back up your Nextcloud's installation and storage.

or, restic is your NAS backup while Nextcloud is your open source dropbox, roughly.