Creating curves programmatically are not supported at this point.
You can approximate arcs manually with a bit of trigonometry, or you can use the GeometryEngine methods to create various forms of ellipses and arcs (I don't know your scenario, but these methods might be what you're really looking for - or not at all):
See doc here:
Thank you for the information. I want to create arcs to make an arc circuit with 4 arcs, similar to bow tie with arcs.
In the Geometry Engine, I did not see any methods to create just arcs like you mentioned. Is there any?
As mentioned no there's no such methods. I listed a set of methods that generates curve-like geometries, in case that was what you were really looking for.
I don't understand what you mean by arc circuits and bow ties. In any case, you'd have to calculate the vertices along the arc yourself to make a polyline that looks curved.