Below is all the linkage and info dump of what I could gather for UNITY multiplayer networking learning and open source resources for github and forums etc, so now go forth and learn how to multiplayer network on unity!
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INFO DUMP:
Note: Important: UNet is a deprecated solution, and a new Multiplayer and Networking Solution (Netcode for GameObjects) is under development. For more information and next steps see the information on the Unity Netcode for GameObjects website. https://docs-multiplayer.unity3d.com/
Click get started and go ahead and start learning.
For documentation here is some more linkage.
The Unity open-source MLAPI solution is being developed to become the new Unity netcode foundation. It is customizable and adaptable for the needs of many multiplayer game types. For more information on this experimental package, see the MLAPI documentation.
Github link above.
Discord link above.
https://forum.unity.com/forums/multiplayer.26/
Unity Forum Link above.
ECS-based networking
For an ECS-based solution, see the DOTS Netcode package. Note: The Entities core system is experimental.
link to ECS github experimental above.