The visuals in the second half made me think of Godot's ambient light, and that it could probably achieve something like this. Unshaded look on illuminated faces, shadowed faces the same but multiplied by ambient color.

I tried to get there with a custom shader using light() but only could really get half of the effect (clamped light color for no over-bright, shadows as full ambient). I couldn't figure out how to multiply by ambient (even leaving diffuse alone), I'd guess that ambient is global post-light() effect. But, I can only pretend to know what I'm doing.

I mean vertex color is already very close and I assume the video itself probably used compositing effects to get the color mix.