According to reverse engineer Jane Manchun Wong, who often comes out with this kind of news, Facebook is working on adding face recognition to the iOS and Android version of Messenger. The data is not sent to Facebook, the description says.
Wong bases the verdict on her own detective work in the code of Facebooks app. The text speaks of Face ID, which is an Apple function, but the text is found in the code of the Android version of the app, which means that the function comes to both Android and iOS.
It is also expected that Facebook will use the system implementations of biometric authentication for Messenger. If that is the case, then Facebook is indeed unable to access the data that is treated by the OS during facial recognition: neither iOS nor Android give that up to apps that use the biometrics -tech.
A screenshot shows that there is the option to lock Messenger after every exit , or a minute, quarter of an hour or hour afterwards. This is to protect personal conversations against viewing by third parties.