This trial is testing branebrutinib, a drug that reduces inflammation, in people with active systemic Lupus Erythematosus (SLE) or Primary Sjögren's Syndrome (pSS). For those with active Rheumatoid Arthritis (RA), the trial will also test if adding abatacept, which prevents immune attacks on the body, provides additional benefits. The goal is to find safer and more effective treatments for these autoimmune diseases.