In scene viewer, and select online applications such as Web Builder, the ability to add the basemap as a layer in the legend to toggle on or off at will is fantastic, especially for applications utilizing underground data such as mining and utility data. However, not all scene-capable applications have this functionality by default, Instant Apps being one of them. One work around I'm currently using is to rely heavily on bookmarks (slides) to control layer visibility, building them in scene viewer so that then transfers to Instant Apps. While this works, I would like the everyday user of this application to simply be able to turn the basemap on and off at will.
My application is built primarily for underground mining data. To combat the incapacity describe above, I've set my basemap transparency in scene viewer to allow a user to "see" underground whenever they are on a bookmark with the terrain turned on, see below - subsurface features just visible beneath the terrain.
Other bookmarks turn the terrain layer off to make the underground layers clearly visible/accessible, however, the basemap gets projected onto a plane at sea level which now inhibits the ability to view/access layers that are below sea level, see below.
Having the ability in scene-derived web apps to toggle the basemap on/off would be a great enhancement to the application of subsurface data.