The purpose of this study is to assess the efficacy and safety of opevesostat plus hormone replacement therapy (HRT) compared to alternative abiraterone acetate or enzalutamide in participants with Metastatic Castration-resistant Prostate Cancer (mCRPC) previously treated with one next-generation hormonal agent (NHA). The primary study hypothesis is that opevesostat is superior to alternative abiraterone acetate or enzalutamide with respect to radiographic progression free survival (rPFS) per Prostate Cancer Working Group (PCWG) Modified Response Evaluation Criteria in Solid Tumors (RECIST 1.1), as assessed by Blinded Independent Central Review (BICR), in androgen receptor ligand binding domain (AR LBD) mutation positive and negative participants.