From Xojo Documentation
| This property is only available on the macOS platform.
For cross-platform compatibility, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this property on an incompatible platform.
The Option key on Mac. This property is Mac-only. If selected, the Option key must be held down while pressing the value of the ShortcutKey property to trigger the event handler of the DesktopMenuItem.
Use DesktopMenuItem.Shortcut to change this value at runtime.