PyQt5 API reference:
http://pyqt.sourceforge.net/Docs/PyQt5/

PySide2:
https://wiki.qt.io/PySide2

In Qt 4.x the client used to receive the winId from server and embed into server. In Qt 5.x the client needs to send its winId to server to embed itself into server. CEF (client) expects winId inside which it will embed. I am not sure it is currently possible to embed CEF in Qt5, unless some workaround/hack is created like for example a temporary hidden window in which CEF will be embedded and then reparented.