One of the factors that make being a product manager difficult at times is the multiple stakeholders that rely on them.
When it comes to the chain of command within a business a product manager would report to their head of the product team, the Chief Product Officer (CPO) for example.
And the CPO reports to the CEO (similar to how the heads of other departments do).
However product managers also report to other stakeholders in their business. Reportng here means providing them with information that their teams need to be enabled for success, not that these stakeholders can make hiring or firing decisions.