How to implement online multiplayer in a simple 1v1 game?

Hello, I want to make my game multiplayer so it can be playable on two devices that are connected to the same network.
My game is pretty simple (two players that use on-screen joysticks to move and a scoring system + a timer that stops the game when the time is over).

Are there any resources on the internet that teach how you can do something like that?
Or if someone has any ideas, I would like to hear them because I really want to learn how to make my game online multiplayer.


I recommend this playlist: Mirror Multiplayer - YouTube

I have some Unity Client + NodeJS server examples at GitHub - CmdrZin/NodeJS: Node.js Server/Client project examples
It’s fairly simple to use.