Found a bug with the difference calculation: When both objects have a height of 0 it generates an error: Boolean operation resulted in empty geometry

What was expected: the difference from the two flat surfaces.
When one of the two objects has a height >0 it works correctly, but of course I wanted a completely flat surface with a cutout.

Even with the error your plugin has already saved me several hours of work. Now I just have to remove all the faces below the top surface with Blender.