This slot will add a new item to the More Tools & Options section.
const { registerPlugin } = wp.plugins;
const { PluginMoreMenuItem,} = wp.editPost;
const MyButtonMoreMenuItemTest = () => (
<PluginMoreMenuItem
icon="smiley"
onClick={ () => { alert( 'Button Clicked' ) } }
>
More Menu Item
</PluginMoreMenuItem>
);
registerPlugin( 'more-menu-item-test', { render: MyButtonMoreMenuItemTest } );