From Xojo Documentation
| This method is only available on platform.
For cross-platform compatibility, use ＃If...＃Endif with the Target... specifiers to make sure you will not attempt to use this method on an incompatible platform.
New in 2019r3
Used by controls that need to know when the style of the OS changes, for example, from light mode to dark mode.
If you implement this interface on your control, you must implement the method as shown here.