Brief Summary: This research study is trying to determine the safety and efficacy of the combination of two oral drugs, abemaciclib and darolutamide, with androgen deprivation therapy (ADT) in the treatment of metastatic, non-metastatic, and advanced prostate cancers. The first phase of the study is to establish a recommended dose for the second phase. The names of the study drugs and interventions involved in this study are: * Darolutamide * Abemaciclib * Androgen deprivation therapy (ADT) - this includes several different treatments, including Gonadotropin-Releasing Hormone (GnRH) antagonists and agonists It is expected that about 93 people will take part in the research study. Treatment is expected to last 6 months with a follow up period of up to 4.5 years.

Detailed Description: This research study is a Phase I/II clinical trial to determine the safety and efficacy of the combination of abemaciclib and darolutamide with androgen deprivation therapy (ADT) in the treatment of metastatic and non-metastatic castration-resistance prostate cancer (CRPC) and for participants with high-risk, localized prostate cancer who will be undergoing radical prostatectomy (RP). A Phase I/II clinical trial tests the safety of investigational drugs with a lead-in phase and attempts to define the maximum tolerated dose of the investigational drugs to use for the second phase. "Investigational" means that the drugs are being studied together for the first time. The names of the study drugs and interventions involved in this study are: * Darolutamide * Abemaciclib * Androgen deprivation therapy (ADT) - this includes several different treatments, including Gonadotropin-Releasing Hormone (GnRH) agonists, Leuprolide and Goserelin, and GnRH antagonist, Degarelix In Phase I, participants will receive abemaciclib in combination with darolutamide and ADT at different dosages. In Phase II, participants will be randomized into two groups of treatment: abemaciclib, darolutamide, and ADT versus darolutamide and ADT. Randomization means that participants are placed into one of the treatment groups by chance, like flipping a coin. The U.S Food and Drug Administration (FDA) has approved androgen deprivation therapy as a treatment for prostate cancer. The FDA has not approved abemaciclib for prostate cancer but it has been approved for other uses. Abemaciclib is approved for use in advanced breast cancer. The FDA has approved darolutamide as a treatment option in men with non-metastatic CRPC but it is not approved in men with metastatic CRPC or localized prostate cancer. Research procedures include screening for eligibility, study treatment including evaluations, blood collection, and radiology scans of the prostate. It is expected about 93 participants will take part in this research study. Treatment is expected to last 6 months with a follow up period of up to 4.5 years. Lilly is supporting this research study by providing funding and the study drug, abemaciclib. Bayer is supporting the study by providing the study drug, darolutamide.