This study is comparing two treatments for **high-risk non-muscle-invasive bladder cancer** (HR-NMIBC). One treatment uses a device called **TAR-210**, and the other uses **intravesical chemotherapy**, which means medicine is put directly into the bladder. The goal is to see which treatment helps people live longer without their cancer returning or getting worse. Participants must have a confirmed diagnosis of HR-NMIBC and a specific gene change called a **fibroblast growth factor receptor** (FGFR) mutation. They should not have muscle-invasive cancer or other active cancers. They also must not have cancer in the bladder lining called **carcinoma in situ (CIS)**. Participants should have had a certain amount of BCG treatment, which is a standard bladder cancer treatment, and be unable or unwilling to have their bladder surgically removed. **Key Points:** - **Duration**: The study length will depend on each participant's condition and response. - **Visits**: Regular check-ups will be required to monitor progress. - **Risks**: Participants must be comfortable with the procedures involved and meet specific health criteria. This study aims to improve treatment options for bladder cancer, but joining is a personal choice and should be discussed with a doctor.