Can we see the shape that is being unwrapped? it looks like you have beveled edges or smooth shading on the object?
The normal map looks accurate then, as far as I can tell. A shape with rounded surfaces will not show as flat in the normal map. I don’t see any seams in your screenshot of the round cube. You can probably want to create your own seams and unwrap it if you are still using the UVs of the original default cube.
You need to have the wire image of the UV editor, the list applied to the modifier, the material setting, etc
These affect baking.
Isn’t the Multires modifier applied. 