It is very common for most teams to first start with filling up the sprint with product backlog items and only after that think about the sprint goal.
That is not the purpose of the Sprint planning. The purpose is to start with a goal and a set of PBIs that the PO think is needed to achieve the goal. After that, if the is still room and the team wants to pull other stuff in, they can do it.
Focusing on output (number of items) instead of outcome (sprint goal) is not the best way to start a sprint.