A Study to Assess Adverse Events and Change in Disease Activity of Intravenously (IV) Infused Etentamig (ABBV-383) in Combination With Anti-Cancer Regimens for the Treatment of Adult Participants With Relapsed/Refractory Multiple Myeloma

Inclusion Criteria: * Eastern Cooperative Oncology Group (ECOG) performance of \<= 2. * Must have confirmed diagnosis of Relapsed/Refractory (R/R) Multiple Myeloma (MM) with documented evidence of progression during or after the participant's last treatment regimen based on the investigator's determination of the International Myeloma Working Group (IMWG) criteria. * Must have measurable disease as determined by central lab as outlined in the protocol. * Must be naïve to treatment with Etentamig. * Must have never received BCMA-targeted therapy. Participants who have received targeted therapy against non-BCMA targets will not be excluded. * Arms A, B and C: Participant has received at least 3 prior lines of MM treatment. * Arm E: Participant has received 1-3 prior lines of MM treatment. Exclusion Criteria: * Received a peripheral autologous stem cell transplant (SCT) within 12 weeks, or an allogeneic SCT within 1 year of the first dose of study treatment. * Unresolved adverse event (AE)s \>= Grade 2 (National Cancer Institute \[NCI\] Common Terminology Criteria for Adverse Events \[CTCAE\] version 5.0) from prior anticancer therapy. * Has any of the following conditions: * Nonsecretory Multiple Myeloma (MM). * Active Plasma cell leukemia i.e., either 20% of peripheral white blood cells or \> 2.0 × 10\^9L circulating plasma cells by standard differential. * Waldenstrom's macroglobulinemia. * Light chain amyloidosis. * Polyneuropathy, organomegaly, endocrinopathy, monoclonal protein and skin changes (POEMS) syndrome. * Major surgery within 4 weeks prior to first dose or planned study participation. * Acute infections within 14 days prior to first dose of study requiring therapy (antibiotic, antifungal or antiviral). * Uncontrolled diabetes or hypertension within 14 days prior to first dose. * Peripheral neuropathy \>= Grade 3 or \>= Grade 2 with pain within 2 weeks prior to first dose.