ONC206 is a new drug being tested to help treat certain types of brain tumors in children and young adults. In this study, doctors want to find the best dose of ONC206 that is safe and effective. They are studying how ONC206 works alone or with radiation therapy in patients with newly diagnosed or recurring (recurrent) brain tumors like diffuse midline gliomas (DMGs) and other central nervous system (CNS) tumors. A diffuse midline glioma is a fast-growing tumor found in the middle of the brain. This drug might help stop the growth of cancer cells by causing a "stress response," which makes cancer cells die but leaves normal cells unharmed.

• The study involves taking ONC206 by mouth for up to 12 months, with possible extension to 24 months if there's a benefit.
• Participants will need to visit the clinic every 28 days during the study and be monitored for side effects.
• This study is for children and young adults aged 2 to 21 years with specific types of brain tumors.

All participants will have regular check-ups for up to 5 years after the treatment to see how well the drug works and ensure safety.