When using the Viewshed widget in Instant Apps it would be amazing if ESRI would expose the elevation and/or height of the handle. It would be really powerful for a user to be able to know at what height above ground, and/or what elevation above sea level they are using the viewshed widget from.
Ideally the ability to select either/or height or elevation would be desirable.
Other ESRI tools which do have this/similar functionality include: the Line of Sight tool - it will report the elevation of features in the graph, and in ArcGIS Earth you can see the elevation ASL (Above Sea Level).