I would like to ask, I simply registered a mousemove event, but when I press alt on the keyboard, this event does not trigger. Is this an internal mechanism of Cesium? If so, is there any way to make mousemove trigger as usual when I press alt
Yes, this is expected behavior.
The mousemove and mousemove when holding the alt key are treated as separate events. The alt key is determined by the modifier parameter when adding an event listener. You can add the same listener to both events to ignore the difference.