Question Built-in shaders package?

From https://docs.unity3d.com/2023.1/Documentation/Manual/shader-Performance.html
"To see the specific simplifications that have been made for each shader, look at the .shader files from the “built-in shaders” package and the information is listed at the top of the file in some comments."

But when I click Built-In shaders it brings me to this page
https://docs.unity3d.com/2023.1/Documentation/Manual/Built-inShaderGuide.html
"Prior to the introduction of the Physically Based Standard Shader, Unity was supplied with more than eighty built-in shaders which each served different purposes. These shaders are still included and available for use in Unity for backwards compatibility but we recommend you use the Standard Shader
wherever possible for new projects."

When I search package manager for "shader" the only thing that comes up is shader graph.

One page says use the built-in shaders package, another page says it's not recommended to use it, and when I search it doesn't exist.

All I want is a starting point to write my own mobile shader.

 

The built-in shaders can be downloaded here: https://unity.com/releases/editor/archive

 

Can I ask what you are referring to on this archive page? Just get a 5.x copy of unity and the shaders are in there?

 

No, I was referring to this (of course, you have to pick the line that matches your Unity version):