From Xojo Documentation
Property (As Integer )
| This property is only available on Windows and Linux platforms.
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.
On Windows and Linux, LineStep is the amount a slider moves when the slider has the focus and the user uses the arrow keys. On macOS it has no effect.