A Product Owner is entitled to postpone the start of a new Sprint after the conclusion of a previous Sprint for the following reason...

This is from Scrum Guide - "A new Sprint starts immediately after the conclusion of the previous Sprint." This is a recommendation you can do whatever you want but then you are doing Scrum.

As a PO I am responsible for making sure that I have Product Backlog ordered for the upcoming Sprint. There can always be some changes, based upon the stakeholder's feedback during the Sprint Review but those should not stop me from starting the Sprint with whatever information I have.

I agree. The team can already start to work on the highest prioritized issues, no matter if a Sprint Goal has officially been decided upon or not.

If I think about in that way it makes sense !, thanks

Suppose after the end of the current sprint (end of the Sprint Retrospective) you delay the start of the new Sprint (Sprint Planning Meeting).
What will the Dev Team do before the new Sprint Planning Meeting ?

According to the Scrum Guide the sprint starts immediately after the previous one. There is no delay. However, if putz of whatever reasons there was no time for a sprint planning yet, I would let the team work in the next prioritized items in the product backlog or let them so some backlog refinement, work on actions resulting from the retrospective, etc. Usually there is always something useful to do 😉

I'm glad this is becoming clearer for you :).

Consider also the lesson this is teaching. Namely, the team's time is valuable to the company and some forethought is required to maximize the value the team creates. PO planning and vision is important and should not hold up the constant value creation of the team.

The planning needed is not be extensive; just enough to keep the team rolling, focused and at a sustainable pace.

> ...a PO with some Product Backlog he has to review to see next but he
> or she is validating against the stakeholders even after sprint review
> because in the Sprint review the stakeholders were a kind of undecided
> about what to do next

That is one of the many unacceptable reasons for delaying a sprint.

A Product Owner is responsible for managing stakeholder involvement, and the release of value to those stakeholders, in a timely fashion. If the Product Owner is not prepared for the next sprint then he or she is remiss in the duties expected of that role.

There may be an "acceptable" reason for a Nexus to delay a sprint, in so far as scrumbling might be needed, although it is a non-canonical practice.