Yes it does increase the vertex count, because each vertex normal requires its own vertex to store the data, same with UV splits. So when you make hard edges you are duplicating vertices. But it’s not that big a deal these days; hardware can handle a lot of vertices.
I made this for a client recently, and it's generic enough that I can share here. So, why not? Here are the source meshes, shaded and in wireframe: When I open hexcube-lowpoly.glb in Babylon.js Sandbox (https://sandbox.babylonjs.com/), the normal map does not represent the beveled high-poly shape from hexcube-highpoly.glb,…