In the default scene with freestyle enabled and external contour selected, I get this:
If I then add a plane below the cube you get this:
Then I enable shadowcatcher on the plane, and get this:
As you can see, the plane affects the line calculation.
So then I move the plane to its own collection and use that collection to exclude the plane from the lineset calculation:
And when I render now, I get this:
So excluding the collection does remove the lines that the plane creates, however it does not allow all of the external contour lines for the cube.
The goal is to have the full contour lines for the cube, zero lines for the shadowcatcher plane, and the shadow sitting underneath - ideally without doing multiple renders and then a composite.
Does anyone know how to make this work?