Additional Study Information: The purpose of this study is to assess the effectiveness and safety of combining an investigational drug called BMS-986218 (also known as Anti-CTLA4-NF monoclonal antibody), or BMS-986218 plus nivolumab, with standard of care docetaxel (chemotherapy), in men who have metastatic castration-resistant prostate cancer (mCRPC) that progressed after a second-generation hormonal manipulation, also known as novel antiandrogen therapy (NAT), and have not received chemotherapy for mCRPC.This study will investigate how participants with mCRPC tolerate these drugs and identify the most suitable dose of BMS-986218 in combination with docetaxel and BMS-986218 in combination with docetaxel and nivolumab. BMS-986218 is an investigational drug that is not approved for a particular use by a local health authority, such as the Food and Drug Administration. Nivolumab and docetaxel have been administered to and are approved for human use in multiple tumor types.