From Xojo Documentation
| This class is only available on the macOS platform.
For cross-platform development, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this class on an incompatible platform.
PrefsMenuItem is designed to handle the Preferences menu item for macOS applications. A menu item derived from the PrefsMenuItem class is automatically moved to the application menu under macOS. Under other operating systems, such a menu item stays where you put it in the Menu Editor.
Since this class is based on MenuItem, please refer to this class for information on its Properties, Methods, and Events.
This class is for creating the Preferences menu item for applications that will run on macOS. Create the menu item under the menu that you want to use for the Windows and Linux builds and then use the Inspector to change its super class to PrefsMenuItem. Otherwise, set up the menu item normally. In your macOS build, it will automatically move to the application menu.
According to Apple user interface guidelines, Cmd+, (comma) is the recommended keyboard shortcut for an application's Preferences menu item.