Flipped Normals as Rendering Mask

so I remember watching a tutorial that enables the function where blender doesn’t render anything behind a face with flipped (red) normal essentially using it as a mask, but I can’t remember how to do it and can’t remember the video itself.

anyone can tell me how to do it?

I think your referring to Backface Culling. I Don’t know what render engine you’re using but in eevee,