The documentations shown here talk about how to backup the related data created and used by the corresponding in-cluster services such as PostgreSQL, Redis and Minio. For the case of using existing external dependent services, it is not covered by this document.
You can follow the guides to backup your data regularly for data protection or only backup data before upgrading or deleting your Harbor cluster.
You can check the data backup guideline for PostgreSQL.
You can check the data backup guideline for Redis.
You can check the data backup guideline for Minio.