Remote Desktop Manager macOS supports different User Interface Styles (sometimes known as skins). These greatly influence the visual aspect of the User Interface as well as its mode of operation. Two styles currently exist:
To select the User Interface style you must go in File - Preferences - User Interface.
The ribbon is Remote Desktop Manager macOS default style that sports an advanced control called ribbon. Icons and text makes it easy to learn what feature exists.
Classic is Remote Desktop Manager macOS previous generation style, it holds a standard menu to invoke commands.