Explanation
The product backlog is a prioritized list of features and requirements that the project team needs to deliver.
The iteration backlog is a subset of the product backlog that the team commits to complete in a given iteration.
Adding a feature that is not part of the MVP to the iteration backlog can disrupt the team's workflow and compromise the quality of the deliverables. Therefore, the project manager should ensure that the feature is added to the product backlog, explain to the sponsor the impact of the request on the team's performance and the project schedule, and ask the team to include the feature's tasks in the next iteration, after they have completed the current iteration's tasks. This way, the project manager can balance the sponsor's expectations and the team's capacity, while maintaining the project's scope and quality. References: PMBOK Guide, PMI Study Hall, PMP Question Bank PMBOK Guide, 7th edition, pages 128-129, 132-133 :
https://www.pmi.org/pmbok-guide-standards/foundational/pmbok