The confusion here comes IMO from the different interpretation and so by users understanding of what an "edge" is in so to say mesh modelers as blender or solid/brep modelers as freecad and then on top of that the additional confusion that actually also in solid modelers the geometry is actually rendered as a mesh and on top of that the shader smoothing (so, brep geometry -> mesh geometry -> shader)...
Here is a video that IMO shows good the concept of "edge smoothing" in blender, understand the difference from the video between smoothing an edge by adding a bevel (adding more polygons) and applying a shader...
This of course is very different to when we talk about faces and their bounding edges in brep and is in general, when we talk about the geometry, also not something we are interested about, but on the coin level this type of shading is also going on in FC and can be seen when changing for example between the "no shading", "shaded" and "flat lines" draw style.
A cylinder in FC and its faces shaded as flat and smooth. This visually represents the brep geometry which is for this cylinder basically just 3 faces (top, bottom and side) and 3 edges (two circles and a seam)
- flat_smooth.jpg (14.1 KiB) Viewed 1004 times
This same cylinder, represented by the coin mesh (polygons), visible in "hidden line" draw style (was renamed to "tessellated" in realthunders version). As we can see a "brep face" is actually represented (rendered to the screen) as many mesh faces (triangles, polygons) and the logic of the normals angles for smooth and flat shading is actually applied between this mesh faces
- coin_mesh.jpg (13.4 KiB) Viewed 1001 times
But if we get back to the edges as represented by boundary lines in FC, if we would be able to use this coin functionality then the logic would be that boundary edges between two smooth shaded faces would be hidden and others (between two flat shaded or between a flat and smooth shaded faces) would be visible...