You mean a post processing effect like this: https://i.imgur.com/9957HgX.png, https://i.imgur.com/eEy6lRR.png?
Its relevantly quite simple yes, there’s even a demo called ‘Stylized Rendering’ that shows how its done.
The cel-shaded shadows are controlled by a material that’s unlit then using a step shading technique from the emissive layer: https://i.imgur.com/P9ATFLr.png
hope this helps.