This study will test an experimental drug named Lenacapavir (LEN), also known as Sunlenca® for the prevention of HIV-1 infection. The other HIV and pre-exposure prophylaxis (PrEP) medication included in this study is F/TDF (brand name Truvada®) which contains emtricitabine (F) and tenofovir disoproxil fumarate (TDF). F/TDF is approved for PrEP for use in adults and adolescents weighing at least 35kg (about 77 pounds) by the FDA in United States. Lenacapavir (LEN) is currently approved by the Food and Drug Administration (FDA) in the United States, Health Canada in Canada, and the European Medicines Agency (EMA) in Europe for the treatment of human immunodeficiency virus (HIV) infection in heavily treatment experienced (HTE) adults with multi-drug resistant (MDR) HIV infection. LEN is currently not approved by FDA or other regulatory authorities for treatment in other HIV populations or for prevention of HIV. LEN is being studied in this study for possible use for prevention of HIV infection.