There currently is one option to travel by night train from Frankfurt (Oder) (Germany) to Przemyśl (Poland), taking between approximately 10 and 11 hours: Namely the EC 431. These lines are operated by Deutsche Bahn and PKP Intercity.
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.
PKP Intercity is Poland's national long-distance railway operator, running domestic and international train services throughout Poland and to neighboring countries.