WebMapViewer.AllowFullScreen

From Xojo Documentation

Property (As Boolean )
aWebMapViewer.AllowFullScreen = newBooleanValue
or
BooleanValue = aWebMapViewer.AllowFullScreen

New in 2020r1

Supported for all project types and targets.

When True provides a widget that allows the user to toggle between the map view consuming the designated space on the page versus consuming the entire browser window.