How to add an applet eg. Brightness indicator applet in Cupertino panel layout in Ubuntu MATE 18.04?

In Cupertino panel layout, I would like to include the brightness applet to the top left next to the wifi, sound and battery applets. How to do that? I find it easier to add in other layouts except in the layouts with the global menu applet.

I don’t use Cupertino, but I just tried it. The way the menu works, I don’t think there’s an easy way. I think your best best it is to right click and remove everything on the right end of the panel, then right click the gap at the end and choose Add to Panel… to add everything back plus the new item(s) you want.