The main purpose of this study is to see how well a new treatment ramantamig-D works compared to standard treatments that is either DVRd or DRd on progression-free survival (PFS; time until a participant's disease worsens) and 12-month minimal residue disease (MRD)-negative complete response (CR) rate (percentage of participants in whom cancer cells are not detected) in participants with newly diagnosed multiple myeloma (NDMM; an initial stage of blood cancer that forms in a type of white blood cells \[WBCs\] called plasma cells) for whom stem cell transplant is not planned as initial therapy.