Which key job function differentiates a Product Manager from a Product Owner (PO)?

One of the key job functions that differentiates a Product Manager from a Product Owner (PO) in SAFe® is prioritizing the backlog. A Product Manager is responsible for defining and prioritizing the features and capabilities that deliver value to the customers and the business. A Product Manager owns and maintains the Program Backlog, which is the single source of truth for the work that needs to be done by the Agile Release Train (ART). A Product Owner, on the other hand, is responsible for defining and accepting the user stories that implement the features and capabilities. A Product Owner owns and maintains the Team Backlog, which is the subset of the Program Backlog that the Agile Team works on. A Product Owner collaborates with the Product Manager to align the Team Backlog with the Program Backlog and the Vision.

References:

Product and Solution Management - Scaled Agile Framework

Product Owner (PO) Sync - Scaled Agile Framework

SAFe Product Manager vs Product Owner - Striking Differences - KnowledgeHut