When scaling Scrum, it is important to have multiple Scrum Teams working from one Product Backlog, because this ensures that they are aligned on the same product vision, goal, and value.
Having one Product Backlog also helps to reduce duplication, inconsistency, and waste, and to optimize the flow of work and feedback. The Product Owner is accountable for managing the Product Backlog and ensuring that it is transparent, ordered, and refined for the multiple Scrum Teams. The Scrum Teams collaborate with the Product Owner and each other to deliver a single integrated product Increment every Sprint.

The Development Team is self-organized, thus manages and decides how to manage their own progress.

One of the primary responsibilities of a Scrum Master is the ability to facilitate regardless of the context or setting.

Explanation
One of the ways to do this is by facilitating the Scrum events, such as the Sprint Review, where the Scrum Team and the stakeholders inspect the product Increment and adapt the Product Backlog2. In this situation, where there is a conflict among the stakeholders about the budget and the funding, your two best options are:
Encourage the stakeholders to focus on delivering the highest value items for the next Sprint.This option aligns with the purpose of the Sprint Review, which is to collaborate on what was done in the Sprint and what to do next2.By encouraging the stakeholders to focus on delivering value, you are helping them prioritize the most important features or functionalities that can maximize the return on investment and reduce risk3. This can also help them align their expectations and goals, and create a shared understanding of the product vision.
Ask for a short break for people to calm down and be objective.This option aligns with your role as a facilitator, who helps the participants have constructive and respectful conversations4. By asking for a short break, you are giving them a chance to cool off and regain their composure. This can also help them be more objective and rational, and avoid emotional reactions that can escalate the conflict or damage the relationship.
The other options are not advisable because:
It is the Product Owner's meeting, so do nothing.This option is incorrect because it contradicts your accountability as a Scrum Master.The Sprint Review is not only the Product Owner's meeting, but a collaborative event that involves the whole Scrum Team and the stakeholders2.As a Scrum Master, you have a responsibility to facilitate this event and ensure that it is productive and valuable1. Doing nothing would mean neglecting your duty and allowing the conflict to persist or worsen.
Defend the budget, asking the stakeholders to support the funding of the work.This option is incorrect because it goes beyond your scope as a Scrum Master.The budget and the funding are not your primary concerns, but rather the value and quality of the product that you deliver1. Defending the budget would mean taking sides in the conflict, which can compromise your neutrality and credibility as a facilitator.
It can also create more tension and resentment among the stakeholders, who may feel that you are not listening to their perspectives or interests.
Argue that the Scrum Team needs to be kept busy while the funding is confirmed.This option is incorrect because it contradicts the principle of empiricism, which is the foundation of Scrum5.Empiricism means that you make decisions based on what is known, rather than what is assumed or predicted5. Arguing that the Scrum Team needs to be kept busy while the funding is confirmed would mean ignoring or denying the reality of the situation, which can lead to waste or inefficiency. It can also undermine the trust and collaborationbetween the Scrum Team and the stakeholders, who may feel that you are not transparent or accountable.
References:1: https://www.scrum.org/resources/what-is-a-scrum-master2:
https://www.scrum.org/resources/what-is-a-sprint-review3:
https://www.scrum.org/resources/blog/value-driven-development4:
https://www.scrum.org/resources/blog/facilitation-scrum-masters-superpower5:
https://www.scrum.org/resources/what-is-empiricism-and-why-is-it-important-to-scrum

The Scrum Team and its stakeholders agree to be open about all the work and the challenges with performing the work.