The mount type for "/" is different in both cases. Since CloudBerry Backup seems to work by mount point, it is possible that it doesn't recognize it.
Under XFS, can you try to run "docker exec CloudBerryBackup mount" ?
From the app's point of view, it's not really important if it is running in a container or not. However, support might be quick to close your case by answering that running in a container is not officially supported.