I know how to rotate an object in Draw.io because usually there is an anchor where my mouse changes into the rotation mode. This is also explained in this tutorial:
However, a curve does not have this option:
Naturally, I could manually move every vertex, but I would prefer to have options to flip/rotate it as a whole.
I tried grabbing the curve with Ctrl, or Alt, or Shift, hoping that it would change from "move object mode" to "rotate object mode" but it does not work that way.