We know in Scrum, the responsible for make estimations is solely responsibility of the development team, but in long term planning, for example a release planning, we'd to have some kind of estimation about all of PBI in order to feed planning burn up or estimates the amount of sprints needed to complete the product.
So is resonsible the Product Owner to make this estimations, and how the PO could perform this in order to make a realistic long term planning?