What is the accountability of the Product Owner during Sprint 0?

Sprint 0 is a term that some organizations use to describe a phase of work before the first official Sprint, where they do some upfront planning, design, architecture, or analysis1. However, this term is not consistent with the Scrum framework, which does not prescribe any pre-Sprint activities or phases2. Scrum starts with a Product Backlog that contains at least one valuable and feasible Product Goal, and enough Product Backlog items to initiate the first Sprint[3][3] . The Product Owner is accountable for maximizing the value of the product and the work of the Developers, and for managing the Product Backlog4. The Product Owner does not have any specific accountability during Sprint 0, because Sprint 0 is not a part of Scrum.