Hi,
The deformation in this example is extremely small. As you’d expect - a 40m long, 10mm diameter steel cable hanging under only its self weight stretches such a tiny amount it isn’t visible (less than 0.2mm over the whole cable), and for most practical purposes the result would probably be considered identical to the standard grasshopper catenary component (which also has it’s own tiny errors, due to the way it is discretized).
If you change the Young’s modulus to, say, 2e+7, to make it a much more stretchy material, you’ll see the difference more clearly.