From Xojo Documentation
| This method 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 method on an incompatible platform.
Because macOS is double-buffered, drawing is accumulated before being shown on screen. You may want to flush the buffer manually after updating a progress bar, drawing the frame of an animation on a canvas, or other things of a similar nature. UpdateNow has no effect on Windows and Linux.