How to recognize rotate in 2D mode on a scene - camrea.changed not fired

CesiumJS
1

I have a scne in 2d wirh enabled rotation

sceneMode: Cesium.SceneMode.SCENE2D,
mapMode2D: Cesium.MapMode2D.ROTATE,

I thought I can recognize the change of the rotation with

camera.changed.addEventListener …

But nothing happened !

Has anyone an idea ?