The purpose of this study is to evaluate the overall survival (length of time from the start of study to date of death from any cause) for pasritamig (JNJ-78278343) in combination with best supportive care (BSC) as compared to placebo with BSC in participants with metastatic castration-resistant prostate cancer (mCRPC; a stage of cancer that has spread beyond the prostate gland and is no longer responding to hormone therapies).