As scrum master, the project manager held spikes to resolve a developer disagreement about how to deliver a feature. What should they do next?

The correct answer is to organize a multivoting event to achieve consensus of the whole team. Multivoting is an effective technique for narrowing down a large list of options to a manageable few, or to reach a decision when there are multiple viable choices and the team needs to agree on one. Since spikes were already held to explore options, the next logical step is to facilitate a team decision. Allowing the team to decide on their own without a structured approach might lead to continued disagreement or an inefficient decision-making process. Organizing more spike events without a clear path to decision-making is inefficient and delays progress. Asking the project sponsor to decide bypasses team autonomy and self-organization, which are core tenets of agile methodologies.