It is nothing to do with HexOS or TrueNAS - you cannot use a Backblaze Personal Computer Backup account to back up a NAS. https://www.backblaze.com/computer-backup/docs/network-attached-storage-nas-devices
If you want to use Backblaze to backup a NAS - any NAS - you need the appropriate account: https://www.backblaze.com/cloud-storage/solutions/nas-backup