Additional Study Information: The purpose of this study is to see if the combination of fianlimab (REGN3767) and cemiplimab (REGN2810) is an effective treatment compared to pembrolizumab in participants that have had melanoma removal surgery but are still at high risk for the return of the disease. This study involves 2 study drugs: fianlimab (REGN3767) and cemiplimab (REGN2810). The study drug, fianlimab is not approved by Food and Drug Administration (FDA). The study drug, cemiplimab, is approved in the FDA for the treatment of advanced cancers but it is considered investigational in this study because it has not been FDA-approved for the treatment of preventing reappearance of melanoma skin cancer following surgery. Pembrolizumab is FDA-approved. However, it is considered investigational in this study because it has not been approved for the treatment of preventing the reappearance of melanoma skin cancer following surgery. Participants will be randomly assigned (by chance; similar to drawing straws) to receive either fianlimab with cemiplimab or pembrolizumab with placebo (a sugar pill or salt water injection). This study is double-blinded. This means that neither you nor the study doctor or the staff will know whether you are being given study drugs (fianlimab plus cemiplimab) or study drug (pembrolizumab) with placebo.