The purpose of this clinical trial is to (1) learn whether the BCMA-CD3 bispecific antibody elranatamab can provide more benefit to people with multiple myeloma compared to a combination therapy including daratumumab, pomalidomide, and dexamethasone, and (2) learn about the safety and activity of elranatamab in combination with the anti-CD38 monoclonal antibody daratumumab. People with multiple myeloma who have received previous treatment including lenalidomide will be enrolled in the study. Part 1 of the study will assess the safety and activity of different doses of elranatamab in combination with daratumumab. People participating in Part 2 of the study will be randomly assigned to receive either elranatamab alone, elranatamab plus daratumumab, or daratumumab, pomalidomide, and dexamethasone. Part 2 will evaluate the safety and activity of (1) elranatamab alone compared to daratumumab, pomalidomide, and dexamethasone, and (2) elranatamab plus daratumumab. Part 3 will assess the effect of increased measures to protect against infection in people treated with either elranatamab alone or together with daratumumab. All people participating in the study will receive study treatment until their disease progresses, they experience unacceptable side effects, or they choose to no longer participate in the study.