Was there anything of that sort made during the gbc era on this hardware ? I thought nobody ever attempted it before

Not exactly this, but many "3D games" were pre-computed scenes. The normal map is the novel bit of this demo.

Ok, and at the time, was anybody even thinking about computing normal maps this way on such hardware ? that was my original though, "maybe" this is the result of applying more recent ideas for this group to hardware that wasn't made to support it. But maybe i'm wrong and people did try.