The study is being conducted in participants that have had surgery and radiation therapy for a type of skin cancer called cutaneous squamous cell cancer (CSCC), and who have a risk that this cancer may come back. The main purpose of the study is to determine if cemiplimab will prevent CSCC from returning after surgery and radiation. Currently, we know that certain types of CSCC have a high chance of coming back after surgery and radiation. At this time, there is no approved treatment to give patients after surgery and radiation to prevent high-risk CSCC from coming back. We are investigating if the addition of cemiplimab will decrease the chance of these high-risk cancers coming back.