From Xojo Documentation

Property (As BevelStyles )
aBevelButton.BevelStyle = newBevelStylesValue
BevelStylesValue = aBevelButton.BevelStyle

New in 2019r2

Supported for all project types and targets.

The bevel style. This property affects the appearance and in some cases the shape of the BevelButton.

The macOS-only bevel styles appear as the Small Bevel style on other platforms.

Bevel styles and appearance varies in general between operating systems and sometimes between versions of operating systems.

Sample Code

This example sets the Bevel property to Round.

Me.BevelStyle = BevelButton.BevelStyles.Round