بسم الله الرحمن الرحيم
A person offering salah alone and the Imam should read only Surah Fatiha in the third rakah of Maghrib. But if one is offering behind an imam then he should not read anything and stay silent.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.