The Scrum Master must understand the principles and values behind agility as well as the Scrum theory.
He/she also must act in ways that reflects the values of Scrum and creates an environment for others to also embrace those values. He/she is responsible for ensuring the team's process stays within the boundaries of the Scrum framework as well as helping and supporting the team with continuous improvement.

The ones that will be doing the work are the best ones to decide on what Development Team structures work best.

Many people misinterpret the Scrum Guide as stating the Development Team size is limited to 3-9 members.
In reality, it only states that there is inherent risk attached to having less than 3 members and more than 9 members. As the number of members increases, the lines of communication also increase. This can be calculated using the Group intercommunication formula: n(n − 1) / 2 where n is the number of members.
Some teams are able to handle the risk and "synergize" whereas others might struggle. Saying that, the relationship between defining a Sprint Goal and Development Team size is unclear.
But the relationship between the ordering of the Product Backlog, the PO having clear objectives, and the Sprint Goal are direct. The Product Owner typically comes to the Sprint Planning with a business objective in mind and Product Backlog items related to the business objective. After deciding what can be done for the upcoming Sprint, the Scrum Team will craft a Sprint Goal that would be met through the implementation of the items. This is not dependent on the size of the team nor length of the Sprint.
Scrum is also a framework that's fit for purpose. Some projects/products are not fit for Scrum... or, better stated, Scrum is not suitable for all projects/products.

The relationship between cause and effect can become more clear when more information emerges.

Using Scrum does not ensure that adding more resources to a project proportionally increases the value delivered. In fact, adding more resources may have the opposite effect, as it can introduce more complexity, communication overhead, coordination challenges, and integration issues. Scrum values quality over quantity, and focuses on delivering the most valuable and feasible outcomes in a given timebox . Scrum also encourages teams to be self-organizing and cross-functional, which means that they can work autonomously and collaboratively without relying on external resources or dependencies.