officially any library part is considered platform-independent, so there is no built-in way within GDL to “know” about the platform.
Could you upload here a win-mac comparison image of the issue you are experiencing with ui_infield? With example code, if possible.
As far as I know, there should be only very small differences, mostly in connection with the control layouts “borrowed” from the platform’s op. system itself. If you see something very different, maybe it’s a bug so I would like to check.
Or maybe we can suggest a workaround:).