From Xojo Documentation

Property (As Picture )
aMobileToolbarButton.Icon = newPictureValue
PictureValue = aMobileToolbarButton.Icon

Supported on Mobile.

Specifies an picture to display for the button's icon.


If you have both a Caption and Icon specified, then only the Icon appears.

Only the mask for the image is used, displayed using the tint color for iOS (currently blue).

For iOS, Apple provides guidelines on icon size.