Check Studio -> Navigation -> System -> Toolbar Member -> Add Content and turn it on. Or you can create custom menus and import the menu. I use Lucid template and created my own custom menus with my own icons. It works well.
The top panel of the Lucid template has been made to use the "inner" top part, that's why "Add more" was removed there. It would be simpler to add one menu point to the Site top menu and set it there to use the Add Content item as sub menu and enable the popup in the settings of this new item. You may see the main settings in the attached screen.