I am quite sure someone has written one or the other network game using GDevelop.
Not being a pro in this - is there some basic code that can be reused or based upon?
I stumbled over a network game tutorial for JMonkeyEngine and that seems quite well designed from my inexperienced point of view: reusable and performant. Somehow I’d love to see something similar for GDevelop…
GDevelop has builtin P2P networking and WebSocket & MQTT networking as extensions. There is a template that shows how to do networking with P2P (Note that it is about the networking, not about the multiplayer!).
The tutorial you linked is about a specific library that is not made for GDevelop, and therefore cannot be used for it.
There is no multiplayer template on GDevelop, you will have to do your own research about how to do multiplayer with your networking options.
P2P networking would be a start. Using websocket and MQTT sounds feasible but that looks like client/server communication to me. After all all the peers do not talk to each other but to the MQTT broker. If that is the case, the broker will just forward the messages either to one or to all peers.
In the JME3 tutorial video I linked the concept is that all clients send their state to the server, which will merge it into a world and broadcast that out to all clients. Maybe that is where the GDevelop solution is called P2P as there is no central server merging all the different states - that work is done on every peer.
Nevertheless I’d like to try that concept. Now how would I use it? Did I link a tutorial or a simple thread in the forum?
Again, as I said, GDevelop only provides networking. Managing your world state, exchanging the updates through the networking method of your choice, displaying that world state, etc… is up to you, as there exist neither templates nor extensions for GDevelop that do any such thing for you.