A Study to Assess Change in Disease Activity and Adverse Events (AE)s in Adult Participants With Immunoglobulin Light Chain (AL) Amyloidosis Receiving ABBV-383 as an Intravenous (IV) Infusion

Inclusion Criteria:

Diagnosis of primary systemic immunoglobulin light chain (AL) amyloidosis.
Eastern Cooperative Oncology Group (ECOG) performance status of <= 2.
Have at least 1 organ historically impacted by AL amyloidosis.
Considered AL amyloidosis risk stage 1, 2, or 3a and have measurable disease of AL amyloidosis as defined by difference between involved and uninvolved free light chains (dFLC) >= 50 mg/L.
Has previously been exposed to a proteasome inhibitor (PI) and an anti-CD38 monoclonal antibody.

Exclusion Criteria:

Known history of clinically significant (per investigator's judgment) drug or alcohol abuse within the last 6 months.
Known allergic reaction, significant sensitivity, or intolerance to constituents of the study drugs (and excipients) and/or other products in the same class.

Participant has the following conditions:

Other non-AL amyloid disease;
Previous or current diagnosis of symptomatic multiple myeloma (MM), including the presence of lytic bone disease, plasmacytomas, >= 60% plasma cells in the bone marrow, or hypercalcemia (defined as corrected calcium > 11 mg/dL);
Active plasma cell leukemia (i.e., either 20% of peripheral white blood cells or > 2.0 × 109/L circulating plasma cells by standard differential);
Waldenström's macroglobulinemia;
Acute diffuse infiltrative pneumopathy;
Major surgery within 28 days prior first dose or planned during study participation;
History of organ transplant requiring continued use of immunosuppressants;
Acute infections within 14 days prior first dose requiring parenteral therapy (antibiotic, antifungal, or antiviral);
Participant has received an autologous stem cell transplant (SCT) within 12 weeks or an allogeneic SCT within 1 year of the first dose of study drug treatment.