A Phase 3 Trial of Fianlimab (Anti-LAG-3) and Cemiplimab Versus Pembrolizumab in the Adjuvant Setting in Patients With Completely Resected High-risk Melanoma

This study is researching an experimental drug called REGN3767, also known as fianlimab (R3767), when combined with another medication called cemiplimab (each individually called a "study drug" or called "study drugs" when combined) compared with an approved medication called pembrolizumab. The objective of this study is to see if the combination of fianlimab and cemiplimab is an effective treatment compared to pembrolizumab in patients that have had melanoma removal surgery but are still at high risk for the recurrence of the disease. Pembrolizumab is an approved treatment in some countries in this clinical setting. The study is looking at several other research questions, including: * What side effects may happen from receiving the study drugs. * How much study drug is in the blood at different times. * Whether the body makes antibodies against the study drug (which could make the drug less effective or could lead to side effects). Antibodies are proteins that are naturally found in the blood stream that fight infections. * How administering the study drugs might improve quality of life.