Question Color Palette Shader

Hey all, I'm trying to make a shader that makes a texture have less colors, for example:
The original texture

And the texture with the shader applied


I would like it to be that I don't havve to give it a color palette, and instead I could set the number of colors it could show. I found a video made by Daniel Ilett that used a Custom Lightning Shader to make the palette but that Custom Lightning shader doesn't seem to work in the newer versions of the shader graph.

the Custom Lightning shader: https://blog.unity.com/technology/custom-lighting-in-shader-graph-expanding-your-graphs-in-2019

 

This is commonly called color quantization / posterization. You might have more luck looking around using those terms.

Here's a simple example:
https://lettier.github.io/3d-game-shaders-for-beginners/posterization.html