MainActivity.cs

    public class MainActivity : AppCompatActivity, IOnMapReadyCallback, ClusterManager.IOnClusterItemInfoWindowClickListener
    {
        private ClusterRenderer m_ClusterRenderer;
        
        //...
    
        public void OnMapReady(GoogleMap map)
        {
            m_map = map;

            //Initialize cluster manager. Setting the CameraIdleListener is mandatory 
            m_ClusterManager = new ClusterManager(this, m_map);
            m_map.SetOnCameraIdleListener(m_ClusterManager);

            //Initialize cluster renderer, and keep a reference that will be usefull for the info window's click event
            m_ClusterRenderer = new ClusterRenderer(this, m_map, m_ClusterManager);
            m_ClusterManager.Renderer = m_ClusterRenderer;
            
            //Custom info window : single markers only (a click on a cluster marker should not show info window)
            m_ClusterManager.MarkerCollection.SetOnInfoWindowAdapter(new CustomGoogleMapInfoWindow(this));
            m_map.SetInfoWindowAdapter(m_ClusterManager.MarkerManager);

            //Handle Info Window's click event
            m_map.SetOnInfoWindowClickListener(m_ClusterManager);
            m_ClusterManager.SetOnClusterItemInfoWindowClickListener(this);

            SetupMap();
        }

        public void OnClusterItemInfoWindowClick(Java.Lang.Object p0)
        {
            //You can retrieve the ClusterItem clicked with a cast
            ClusterItem itemClicked = (ClusterItem)p0;

            Toast.MakeText(this, "Info Window clicked !", ToastLength.Short).Show();

            //Dismiss the info window clicked
            m_ClusterRenderer.GetMarker(itemClicked).HideInfoWindow();
        }
    }