This study is for people with relapsed or refractory multiple myeloma (RRMM), a type of cancer that affects plasma cells in the bone marrow. The study compares two treatments: IberDd (using iberdomide, dexamethasone, and daratumumab) and DVd (using daratumumab, bortezomib, and dexamethasone). It's an open-label study, meaning participants know which treatment they are receiving. The study is conducted in two stages with up to 864 people participating. In the first stage, 200 people are randomly assigned to different doses of iberdomide or the DVd treatment. In the second stage, 664 more participants are randomly placed into either the IberDd or DVd groups. Treatment continues until the disease worsens or other reasons like side effects or quitting. The study follows International Council for Harmonisation (ICH) and Good Clinical Practices (GCPs) guidelines.

• Participants must have tried 1-2 previous treatments for multiple myeloma.
• Participants will be followed for disease assessment after stopping treatment.
• People with other specific health conditions are not eligible to join.