Rendering 3D objects to look 2D

I'm using pro version of Unity, I have a 3D project which uses cel-shading. I'm good at 3D modelling, but terrible with 2D art.

I want my 3D objects to have a retro 2D 8bit sort of appearance. Preferably I want this to be rendered to appear as 2D, not converting 3D to 2D sprite sheets because I think the latter would limit shading effects.

Are there any tutorials or assets which can achieve such an effect?

I've been searching Google for something like this but it's really difficult to find anything relevant.

The best example I've found is from this reddit thread which links to this website which has a unity player for previewing their pixelated 3D project, but there's no further information on this. The author apparently said they're going to make a tutorial for it but that was 4 years ago and there's been no update since. This is the exact effect I'm trying to achieve, but nobody seems to know how it's done.