Backup-Problem on Synology DS

NC Version 30.0.2
I have a strange problem for which I cannot find a solution so far. Nextcloud is running on a NAS (Synology DS), the Nextcloud data is stored in a separate folder (nc-data).

When I give my admin user permission for this folder (to back up the data using hyper backup), this permission is gone again after a few minutes, obviously Nextcloud keeps revoking the permission.

I’m not sure, is this a Nextcloud issue, or a Synology issue?

Anyway, I can’t create an automatic backup this way.

Does anyone have an idea how to create a backup here in a meaningful way?

Thanks for your feedback
Rudolf