This phase II trial tests how well lenalidomide and epcoritamab works in treating patients with follicular lymphoma that has not been previously treated. Although follicular lymphoma is incurable, prognosis has improved for both early and advanced stage disease, largely attributed to therapeutic advances. Lenalidomide may stimulate or suppress the immune system in different ways and stop cancer cells from growing and by preventing the growth of new blood vessels that cancer cells need to grow. Epcoritamab is a bispecific monoclonal antibody that binds to two different antigens (the part of the target that the antibody attaches to), at the same time. This dual action allows bispecific antibodies to improve target specificity by binding two antigens on the same cell to recruit and activate immune cells to kill cancer cells. Lenalidomide and epcoritamab, when given together, may be more effective in treating patients with follicular lymphoma than if they were given alone.