Inclusion Criteria: - Relapsed or refractory multiple myeloma (MM) and must: 1. have documented disease progression during or after their last myeloma therapy 2. be refractory to, intolerant to, or not a candidate for available, established therapies known to provide clinical benefit in MM - Must have measurable disease - Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 or 1 - Agree to follow the CC-92480 Pregnancy Prevention Plan (PPP) Exclusion Criteria: - Known active or history of central nervous system (CNS) involvement of MM - Plasma cell leukemia; Waldenstrom's macroglobulinemia; polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes (POEMS) syndrome; or clinically significant light-chain amyloidosis. - Impaired cardiac function or clinically significant cardiac disease - Previous SARS-CoV-2 infection within 14 days for asymptomatic or mild symptomatic infections or 28 days for severe/critical illness prior to Cycle 1 Day 1 (C1D1) - For Part 1: received prior therapy with CC-92480 - For Part 2: received prior therapy with CC-92480, tazemetostat, BMS-986158, or trametinib - Previously received allogeneic stem-cell transplant at any time or received autologous stem-cell transplant within 12 weeks of initiating study treatment - Received any of the following within 14 days prior to initiating study treatment: 1. Plasmapheresis 2. Major surgery 3. Radiation therapy other than local therapy for myeloma associated bone lesions 4. Use of any systemic anti-myeloma drug therapy - Used any investigational agents within 28 days or 5 half-lives (whichever is shorter) prior to initiating study treatment - COVID-19 vaccine within 14 days prior to C1D1 Other protocol-defined inclusion/exclusion criteria apply