A Study to Assess the Efficacy, Safety and Tolerability of DDY391 in Participants With Moderate to Severe Psoriatic Arthritis

Key Inclusion Criteria: * Female or male participants at least 18 years of age. * Diagnosis of PsA and meeting classification criteria for Psoriatic arthritis (CASPAR) at screening. * Moderate to severe PsA at screening and baseline. Key Exclusion Criteria: * Presence of inflammatory conditions other than psoriasis or PsA including but not limited to those associated with arthralgia or arthritis (e.g., rheumatoid arthritis, systemic lupus erythematosus, scleroderma, sarcoidosis) or presence of fibromyalgia or osteoarthritis with articular symptoms. * Use of bDMARD treatment within 4 weeks or 5 half-lives of randomization, whichever is longer * Prior use of JAK inhibitors or TYK2 inhibitors (e.g., deucravacitinib). Prior use of apremilast is allowed but must not be taken within 4 weeks of baseline. * Previous treatment with any cell-depleting therapies, including but not limited to anti-CD20, unless ≥ 12 months prior to baseline. * History of lymphoproliferative disease or any known malignancy or history of malignancy of any organ system within the past 5 years (except for basal cell carcinoma or actinic keratosis that have been treated with no evidence of recurrence in the past 3 months, carcinoma in situ of the cervix or non-invasive malignant colon polyps that have been removed). * Any active viral, bacterial or other infections at the time of screening or randomization, or history of recurrent clinically significant infection or of recurrent bacterial infections. Other protocol-defined inclusion/exclusion criteria may apply.