By default, backups use the storage policy of the subclient to back up SQL Always On availability groups.
Note
Inline copies of SQL Always On availability group backups with a region-based storage policy are not supported.
You can back up SQL Always On availability groups by using a backup plan with region-based storage enabled that is in the same region as the replica of the availability group that is selected for backup.
For information about region-based storage and configuration, see Region-Based Storage for Laptop and Backup Plans.