The client is using an unsupported version of the Socket.IO or Engine.IO protocols Error
There appears to be some backward compatibility issues with SocketIO. You can uninstall python-engineio, python-socketio (and Flask-SocketIO just to be on the safe side) and reinstall lower versions. The combination that worked for me was: Flask-SocketIO==4.3.1 python-engineio==3.13.2 python-socketio==4.6.0