From Xojo Documentation
Supported PlatformsProject Types: Desktop Platforms: macOS
Applies the selected button style to the PushButton. This is a macOS-only property. You can only set the ButtonStyle Property in the IDE, not in code.
The styles are not shown in the Layout Editor in the IDE, but you'll see them in your macOS app when you run it.
ButtonStyle accepts the following values:
|9||Help, leave the Caption property blank.|