Is there a good way to learn how to develop multiplayer games?

Greetings to all!
Unity allows me to do the following:
Featuring a character and a simple setting (Character and Scene)
This is an easy 2D game (with a character and a scene)
Creating an interface
What is the C# programming language? What programming language does it use?
The most interesting games for me are multiplayer games (online multiplayer).
My motivation for learning more will be sparked if that happens.
So what basics do you think, I should have before tackling that? And especially what tutorials/documentations could you recommend?
What are the alternatives to photon? It's hard for me to know where to begin.
I appreciate your help.

 

I'd follow basic tutorials first (from unity learn and youtube, for general stuff and c# too)

For photon there are lots of examples and tutorials, so could be easy to follow those first.

Some alternatives are:
- Networking for GameObjects https://unity.com/products/netcode (from unity, but its still quite new..)
- Mirror https://github.com/vis2k/Mirror
- Fishnet https://github.com/FirstGearGames/FishNet