CorvaNocta Is there a place to check out the basics of networking for Godot 4?
If you want simple low-level raw byte (or text) communication, check out the WebSocketClient and WebSocketServer examples.
They might be slightly outdated already, but should work fine for Godot 4.X. (maybe minor adjustments are needed)
Godot 3.X had a even simpler WebSocket implementation, but it was replaced with the examples I linked for some reason.
It's pretty much as simple as creating a server, calling server.listen(port) and polling for events such as incoming data or a new client attempting to connect.
Same on the client: create it, call client.connect(url) and poll for events such as disconnect or received data.
What exactly you send and receive that way is up to you then.