This study will test a new investigational cellular therapy product called Bemdaneprocel (stem cell derived neuronal cells) for people with Parkinson’s Disease who have 2.5 hours or more of daily OFF time. Patients are randomized to either stem cell therapy or placebo. The goal is to improve long-term PD management by improving their ability to move, slowing the disease's progress, and enhancing their quality of life. It also seeks to do this with fewer side effects than current treatments.