Here we use a different color (Fill Color) as fill color, a different color on the outer edge (Outline color), size of the symbol (symbol size), one symbol (symbol) and a width of the outer edge (Width).
For clustering, it is indicated that the ellipse will be Criteria (Region) and that the distance between the real objects, points, from Criteria shall be maximum 40 px (Max distance).
In addition, it entered any label for points, one label that will print the number of points that each cluster comprises. This is done by selecting one appearance on the label (Label style) and specify what is to be printed “[Cluster: Feature Count],” which is one expression of the number.
Example on legend
Example on map