fix

Runtime/engine/UIWidgetsPanel.cs

         }
 
         int getMouseButtonDown() {
+            //default mouse button key = left mouse button
+            var defaultKey = 0;
-                    return InputUtils.getMouseButtonKey(key);
+                    defaultKey = key;
+                    break;
-
-            return 0;
+            return InputUtils.getMouseButtonKey(defaultKey);
         }
 
         public void OnPointerDown(PointerEventData eventData) {

Runtime/gestures/events.cs

                 position: position,
                 down: false) {
         }
+        
+        public static PointerHoverEvent fromHoverEvent(PointerEvent hover) {
+            return new PointerHoverEvent(
+                timeStamp: hover.timeStamp,
+                pointer: hover.pointer,
+                kind: hover.kind,
+                device: hover.device,
+                position: hover.position
+            );
+        }
     }
 
     public class PointerEnterEvent : PointerEvent {
                 down: false) {
         }
 
-        public static PointerEnterEvent fromHoverEvent(PointerHoverEvent hover) {
+        public static PointerEnterEvent fromHoverEvent(PointerEvent hover) {
             return new PointerEnterEvent(
                 timeStamp: hover.timeStamp,
                 pointer: hover.pointer,

Runtime/gestures/mouse_tracking.cs

                 if (!hitAnnotation.activeDevices.Contains(deviceId)) {
                     hitAnnotation.activeDevices.Add(deviceId);
                     if (hitAnnotation.annotation?.onEnter != null) {
-                        hitAnnotation.annotation.onEnter(PointerEnterEvent.fromHoverEvent((PointerHoverEvent)lastEvent));
+                        hitAnnotation.annotation.onEnter(PointerEnterEvent.fromHoverEvent(lastEvent));
-                    hitAnnotation.annotation.onHover((PointerHoverEvent)lastEvent);
+                    hitAnnotation.annotation.onHover(PointerHoverEvent.fromHoverEvent(lastEvent));
                 }
 
                 foreach (_TrackedAnnotation trackedAnnotation in this._trackedAnnotations.Values) {