Multiple myeloma (MM) is a cancer of the blood's plasma cells. The cancer is typically found in the bones and bone marrow (the spongy tissue inside of the bones) and can cause bone pain, fractures, infections, weaker bones, and kidney failure. Treatments are available, but MM can come back (relapsed) or may not get better (refractory) with treatment. This is a study to determine the safety, efficacy, and pharmacokinetics of Etentamig in adult participants with MM. Etentamig is an investigational drug being developed for the treatment of MM. This study is broken into 4 substudies and each substudy consists of a dose escalation phase and dose expansion phase. Participants will receive escalating doses of etentamig alone or in combination with daratumumab and lenalidomide (DR), carfilzomib and dexamethasone (Kd) or lenalidomide (R). This will be followed by etentamig at the dose levels established during the escalation phases alone or in combination with DR, Kd, R. The participants can also receive daratumumab, lenalidomide and dexamethasone (DRd), R, or daratumumab, carfilzomib, and dexamethasone (DKd) as a comparator in the dose expansion phases. Around 440 adult participants with MM will be enrolled at approximately 50 sites worldwide In all substudies, participants will receive escalating doses of etentamig as Intravenous (IV) infusions, alone or in combination with DR, R or Kd, followed by IV infusions of etentamig at the dose levels established during the escalation phases alone or in combination with IV and oral DRd, DKd, or R. The study duration is approximately 130 months. There may be higher treatment burden for participants in this trial compared to their standard of care. Participants will attend regular visits during the study at a hospital or clinic. The effect of the treatment will be checked by medical assessments, blood tests, checking for side effects and questionnaires.