Situations to work through: a PO who will not prioritise, a team that skips retros, mid-sprint scope injection.
3 questions in Agile, Scrum & Delivery.
Do not argue about priority in the abstract; make the cost of not choosing visible by showing capacity against the ask, then force a decision through a mechanism that requires ordering rather than asking for agreement.
Make the shortfall visible today, then have the Developers and Product Owner renegotiate scope against the Sprint Goal, which is the commitment while the item list is not. Finish work in progress, keep the Sprint length fixed, and return what is unfinished to the Product Backlog for reordering.
Do not open with the Scrum Guide. Show what pre-assignment costs in flow terms, since assigning everyone an item on day one puts the whole Sprint in progress at once and stretches cycle time. Then find out what the manager needs from it and offer a mechanism that meets that need without the assignment.