This is a simple shader gradient map that I like to use based on the one AzizDraws made in their video here: https://www.youtube.com/watch?v=R022uQR2akA&t=2s.
The first one is the exact one he uses in the video, the second one is my preferred edit.
You can do this in any way that best fits your style and work flow, this is the way that I use it.
First, I set up my flat colors:

Then, I make a shading folder (set to normal) and shade with a white base layer, a grey mid layer, and a black layer:


Once I've done that, I set my layer folder to either Darken, Multiply, or Overlay, its up to you and your image. This one, I set to darken.
I then make a gradient map layer by going to the top bar and selecting Layer > New Correction Layer > Gradient Map and then selecting the one I wish to use, this one used Shader 2.

After that I mess with the grey and black layer's opacities until I Like how it looks.

When that's done, I filter and highlight until I like how it looks

Easy Peasy :)
First, I set up my flat colors:

Then, I make a shading folder (set to normal) and shade with a white base layer, a grey mid layer, and a black layer:


Once I've done that, I set my layer folder to either Darken, Multiply, or Overlay, its up to you and your image. This one, I set to darken.
I then make a gradient map layer by going to the top bar and selecting Layer > New Correction Layer > Gradient Map and then selecting the one I wish to use, this one used Shader 2.

After that I mess with the grey and black layer's opacities until I Like how it looks.

When that's done, I filter and highlight until I like how it looks

Easy Peasy :)