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.