A Study of JNJ-79635322 in Participants With Relapsed or Refractory Multiple Myeloma or Previously Treated Amyloid Light-chain (AL) Amyloidosis

Inclusion Criteria:

For participants with relapsed or refractory multiple myeloma:

Have a documented initial diagnosis of multiple myeloma according to International Myeloma Working Group (IMWG) diagnostic criteria
Have relapsed or refractory disease, have been treated with a proteasome inhibitor, immunomodulatory drug (IMiD) agent, and an anti-CD38-based therapy for the treatment of multiple myeloma (MM), and should have been treated with at least 3 prior lines of therapy, or are refractory to proteosome inhibitor, IMiD agent, and an anti-CD38-based therapy regardless of prior lines of therapy
Must have an Eastern Cooperative Oncology Group (ECOG) status of 0 or 1
Have measurable disease at screening as defined by at least 1 of the following: a) Serum M-protein level greater than or equal to (>=) 0.5 grams per deciliter (g/dL); or b) Urine M-protein level >=200 milligrams (mg)/24 hours; or c) Light chain multiple myeloma: Serum immunoglobulin (Ig) free light chain (FLC) >=10 milligrams per deciliter (mg/dL) and abnormal serum Ig kappa lambda FLC ratio; d) For participants without measurable disease in the serum, urine, or involved FLC, presence of 1 or more focus of extramedullary disease (EMD) which meets the following criteria: extramedullary plasmacytoma not contiguous with a bone lesion, at least 1 lesion >=2 centimeter [cm] (at its greatest dimension) diameter on whole body Positron Emission Tomography and Computed Tomography (PET-CT) Scans (or whole body magnetic resonance imaging [MRI] approved by sponsor), and not previously radiated

For participants with previously treated AL amyloidosis:

Initial histopathological diagnosis of amyloidosis
Participant who is not a candidate for available AL amyloidosis therapy with established clinical benefit and should have received at least 3 cycles of 1 prior line of therapy or a total of at least 2 cycles of 2 or more prior lines of therapy for AL amyloidosis
Measurable disease at screening defined by at least 1 of the following: serum involved free light chain (iFLC) >=50mg/L or difference between involved and uninvolved free light chains (dFLC) >=50mg/L, or serum m-protein >= 0.5g/dL
One or more organs impacted by systemic AL amyloidosis
Left ventricular ejection fraction (LVEF) >=45%

Exclusion Criteria:

For participants with relapsed or refractory multiple myeloma:

Central Nervous System (CNS) involvement or clinical signs of meningeal involvement of multiple myeloma. If either is suspected, brain magnetic resonance imaging (MRI) and lumbar cytology are required
Active plasma cell leukemia, Waldenstrom's macroglobulinemia, POEMS syndrome (polyneuropathy, organomegaly, endocrinopathy, M-protein, and skin changes), or primary light chain amyloidosis
Received a cumulative dose of corticosteroids equivalent to greater than (>) 140 mg of prednisone within the 14-day period before the start of study treatment administration
Prior antitumor therapy within 21 days prior to the first dose of study treatment (proteasome inhibitor [PI] therapy or radiotherapy within 14 days, immunomodulatory drug (IMiD) agent therapy within 7 days, gene-modified adoptive cell therapy within 90 days, or CD3-redirecting therapy within 21 days)
Prior allogeneic transplant within 6 months before the start of study treatment administration or autologous transplant within 12 weeks before the start of study treatment administration
Live, attenuated vaccine within 4 weeks before the first dose of study treatment
Non-hematologic toxicity from prior anticancer therapy that has not resolved to baseline levels or to Grade less than or equal to (<=) 1 (except alopecia, tissue post-RT fibrosis [any grade] or peripheral neuropathy to Grade <=3)
The following medical conditions: pulmonary compromise requiring supplemental oxygen use to maintain adequate oxygenation, human immunodeficiency (HIV) infection, active hepatitis B or C infection, stroke or seizure within 6 months prior to first dose of study treatment, autoimmune disease, serious active viral or bacterial infection, uncontrolled systemic fungal infection, cardiac conditions (myocardial infarction <=6 months prior to enrollment, New York Heart Association stage III or IV congestive heart failure, et cetera)

For participants with previously treated AL amyloidosis:

CNS involvement or clinical signs of meningeal involvement of AL amyloidosis. If either is suspected, whole brain MRI and lumbar cytology are required
Any form of non-AL amyloidosis, including but not limited to transthyretin (ATTR) amyloidosis
Active plasma cell leukemia, Waldenstrom's macroglobulinemia, or POEMS syndrome
Pulmonary compromise requiring supplemental oxygen use
Any serious medical conditions such as: active viral, bacterial, fungal infection; active autoimmune disease; HIV infection, active hepatitis B or C infection, stroke or seizure within 6 months prior to first dose of study treatment, significant cardiovascular conditions
Previous or current diagnosis of symptomatic multiple myeloma
Macroglossia that impairs swallowing difficulty
Received a cumulative dose of corticosteroids equivalent to > 140 mg of prednisone within the 14-day period before the start of study treatment administration
Prior antitumor therapy within 21 days prior to the first dose of study treatment (PI therapy or radiotherapy within 14 days, IMiD agent therapy within 7 days, gene-modified adoptive cell therapy within 90 days, or CD3-redirecting therapy within 21 days)
Prior allogeneic transplant within 6 months before the start of study treatment administration or autologous transplant within 12 weeks before the start of study treatment administration
Live, attenuated vaccine within 4 weeks before the first dose of study treatment
Non-hematologic toxicity from prior anticancer therapy that has not resolved to baseline levels or to <=1 (except alopecia, tissue post-RT fibrosis [any grade] or peripheral neuropathy to Grade <=3)