A Study Evaluating Ficerafusp Alfa (BCA101) QW in Combination With Pembrolizumab vs Alternative Ficerafusp Alfa Dosing in 1L R or M HNSCC

Inclusion Criteria: * Age ≥18 years on the day the Informed Consent Form is signed. * Histologically or cytologically confirmed R or M HNSCC. Eligible primary tumor locations are oral cavity, hypopharynx, larynx or oropharynx (with documented HPV-negative disease if presenting with OPSCC). Note: primary tumor location of paranasal sinuses and nasopharynx, any histology are excluded. * No prior systemic therapy administered in the R or M setting; and completed systemic therapy \>6 months prior if given as part of multimodal treatment for locoregionally advanced disease in the adjuvant or definitive setting. * Archival tumor tissue or willing to undergo pretreatment biopsy at Screening if archival tissue is insufficient or unavailable. * PD-L1 CPS ≥1. * Measurable disease based on RECIST 1.1. * Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1. * Adequate organ function, as defined in the protocol. Exclusion Criteria: * Disease suitable for local therapy administered with curative intent. * Prior treatment with anti-TGFβ therapy. * Prior therapy with an anti-EGFR antibody (exception: radio sensitizing agents and multimodal treatment for locoregionally advanced disease). * Prior history of Grade ≥2 intolerance or hypersensitivity reaction to anti-EGFR therapy or other murine proteins. * Prior therapy with an immune checkpoint inhibitor completed within 6 months prior to study treatment initiation. * Progressive disease \<6 months from completion of curative intent systemic therapy for locoregionally advanced HNSCC. * Life expectancy less than 3 months. * Known active central nervous system metastases, history of spinal cord compression from tumor involvement, a history of carcinomatous meningitis, or leptomeningeal disease are excluded. * Current active major bleeding, or a recent major bleeding episode within 4 weeks prior to enrollment. * Subject participated in another clinical study or received treatment with another investigational drug must wait at least 5 half-lives of the treatment received or 4 weeks (whichever is shorter) following prior therapy. * Active autoimmune disease requiring systemic treatment in the past 2 years. * Subjects with chronic hepatitis B virus (HBV) infection with active disease who meet the criteria for anti-HBV therapy and are not on a suppressive antiviral therapy prior to initiation of study treatment. * Subjects with a known history of hepatitis C virus (HCV) who have not completed curative antiviral treatment or have an HCV viral load above the limit of quantification at Screening. * Known history of human immunodeficiency virus (HIV). * Receipt of any organ transplantation, including autologous and allogeneic stem cell transplantation, with the exception of transplants that do not require immunosuppression. * Known to be diagnosed and/or treated for any other additional malignancy within 2 years prior to randomization with the exception of the following: curatively treated basal cell carcinoma or squamous cell carcinoma of the skin, and curatively resected in situ cervical cancer, and curatively resected in situ breast cancer, and low-risk early stage prostate cancer. * Any condition requiring systemic treatment with either corticosteroids (\>10 mg daily of prednisone or equivalent) or other immunosuppressive medication within 7 days prior to the first dose of study treatment, except for topical, intranasal, intrabronchial, or ocular steroids. * Use of a live or live attenuated vaccine within 4 weeks prior to Screening.