Hi
when you define/create a new policy in the AG setting section you can select to:
Backup on preferred backup replica only - Select this option to backup only on preferred backup replica. The preferred backup replica is decided by the backup preferences configured for the AG in the SQL Server
Select replicas for backup - Choose the primary AG replica or the secondary AG replica for the backup.
Backup priority - Specify a minimum backup priority number, and a maximum backup priority number that decide the AG replica for backup.
is that what you need?
bye