ToolbarButton.Pressed

From Xojo Documentation

Property (As Boolean )
aToolbarButton.Pressed = newBooleanValue
or
BooleanValue = aToolbarButton.Pressed

New in 2019r2

Supported for all project types and targets.

True if the ToolbarButton was pressed. It can be used to set the toggled state of a toggle-style ToolbarButton at runtime.