A Trial to Learn if Odronextamab is Safe and Well-Tolerated and How Well it Works Compared to Rituximab Combined With Different Types of Chemotherapy for Adult Participants With Previously Untreated Follicular Lymphoma

This study is researching an experimental drug called odronextamab, referred to as study drug. The study is focused on participants with previously untreated follicular lymphoma (a type of non-Hodgkin lymphoma or NHL). This study will be made up of two parts: Part 1 (non-randomized) and Part 2 (randomized - controlled). The aim of Part 1 of the study is to see how safe and tolerable the study drug is when given alone. The aim of Part 2 of the study is to see how the study drug works compared to rituximab (called the "comparator drug") and chemotherapy (the current standard of care for NHL). Standard of care means the usual medication expected and used when receiving treatment for a condition. The study is looking at several other research questions, including: * What side effects may happen from taking the study drug * How much study drug is in the blood at different times * Whether the body makes antibodies against the study drug (which could make the study drug less effective or could lead to side effects) * How the study drug affects quality of life and ability to complete routine daily activities.

Key Inclusion Criteria: 1. Diagnosis of Cluster of Differentiation 20\^+ (CD20\^+) FL Grade 1-3a, stage II bulky or stage III / IV 2. Need for treatment as described in the protocol 3. Have measurable disease on cross-sectional imaging documented by diagnostic imaging Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) 4. Eastern Cooperative Oncology Group (ECOG) performance status of 0-2 5. Adequate bone marrow function and hepatic function, as described in the protocol Key Exclusion Criteria: 1. Central Nervous System (CNS) lymphoma or leptomeningeal lymphoma 2. Histological evidence of transformation to a high-grade or diffuse large B-cell lymphoma 3. Waldenström Macroglobulinemia (WM, lymphoplasmacytic lymphoma), Grade 3b follicular lymphoma, chronic lymphocytic leukemia, or small lymphocytic lymphoma 4. Treatment with any systemic anti-lymphoma therapy 5. Infections and allergy/hypersensitivity to study drug or excipient, as described in the protocol NOTE: Other protocol defined inclusion/exclusion criteria apply