You don't have write permission to backup destination

Debian 12, using whatever the built-in backup system is. I have it set to back up to an external drive that's dedicated to this purpose. When I hit the button to do a backup, it says I don't have write permission. I have verified indeed, I can't create a file or folder on that drive without using sudo. How do I grant myself and the backup process the access it needs to do a backup? Thanks. Selected backup drive: Go button and resulting error: Edit with requested details: - root owns it - Dolphin says Ower can view & modify, group and others can only View. - Was ExFAT, reformatted to ext4, now that button does nothing but the *other* backup dialog says "Giving up after 5 attempts. Error: Error opening file “/backup/duplicity-full.20240802T203854Z.vol1.difftar.gz”: Permission denied"