Thanks so much for your help, but that's not actually what I was asking about.
So I want to make an online multiplayer on Steam WITHOUT using the Steam Networking.
I was looking for the documentation about Steam Networking, and I've found this:
Does your game already have networking?
If your game is peer-to-peer then all you need to do is integrate Steam Matchmaking & Lobbies with your networking to provide a great experience for Steam users.
This is on Steamworks Documentation, and it's here: https://partner.steamgames.com/doc/features/multiplayer#matchmaking
So I think there's probably a way to make this work, but I could not find a way to do so. I was successfully make a lobby using Steam Lobby & Matchmaking, but could not find a way to make them connect together using Godot HL Networking instead of using Steam Networking. So is there a way to do so?
Edit: Hi, I'm a little bit stressful at the moment, so I'm really apologize if I'm somewhat sound rude to you, but I really appreciate by your help.