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. Follicular lymphoma is a type of non-Hodgkin lymphoma or NHL. Participants with follicular lymphoma that has come back after treatment (called relapsed) or did not respond to treatment (called refractory) are eligible to take part only in Part 1A of the study. This study is made up of 3 parts: Part 1A (non-randomized), Part 1B and Part 2 (randomized - controlled). The aim of Part 1A and Part 1B of the study is to see how safe and tolerable the study drug in combination with chemotherapy is and to determine the dose and schedule of the study drug to be combined with chemotherapy to be used in Part 2 of the study. The aim of Part 2 of the study is to assess how effective the combination of the study drug with chemotherapy is in comparison with the combination of rituximab 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) * The impact from the study drug on quality-of-life and ability to complete routine daily activities