In the Nexus guide it says: "A Nexus works off a single Product Backlog, and as described in the Scrum framework, a Product Backlog has a single Product Owner who has the final say on its contents. The Product Owner is responsible for maximizing the value of the product and the work performed and integrated by the Scrum Teams in a Nexus. The Product Owner is a member of the Nexus Integration Team." This seems to imply that a Nexus only has 1 product owner and no additional product owners in the teams. Is this correct? The guide is a bit vague about this and You can wonder how this would work with 9 scrum teams in a Nexus.
If there is a single Product and a single Product Backlog, there is one Product Owner. There are multiple Scrum Teams working on the same product, the Product Backlog remains a single source of requirements and it is owned by one Product Owner.
In Scrum there is one Product Owner and one Product Backlog for one product. Scrum Teams working on the same product will integrate their work in the same Nexus and thereby provide value to the same Product Owner.