Hello, this is a small program that should demonstrate that multiplayer also works in the BGE. Befor one starts the Blender script one must start the server (server.py). When you want to edit this game on your PC edit it in server/data/ not in client/client-data/ otherwise it will deleted when you start the client.
it is possible to update the BGE network Multiplayer Blender 2.7 that it works under UPBGE Blender 2.83
I didn't used UPBGE. But I can recommend the godot game engine. It's own programm language is similar to python. https://godotengine.org/
Im on android right now, but damn, if this is well written, then I just might have to finish that game I gave up recently!