There currently is one option to travel by night train from Frankfurt am Main (Germany) to Stendal (Germany), taking between approximately 6 and 7 hours: Namely the ICE 1272 operated by Deutsche Bahn.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night.
These trains only have first and second class seats. The cars remain lit throughout the night and the seats cannot be reclined.