From Xojo Documentation
New in 2021r3
The Quit menu item is derived from the DesktopQuitMenuItem class.
The Quit menu item that is added by default to all applications is an instance of the DesktopQuitMenuItem class. It differs from menu items derived from the DesktopMenuItem class in that it is enabled by default and automatically calls the Quit method to quit the application. Thus, there is no need to enable the menu item via code or write its handler.
On macOS, instances of DesktopQuitMenuItem are moved to the Application menu for you automatically. This prevents multiple DesktopQuitMenuItem entries from appearing in menus (only the first usage appears).