Hi Bob et al,
((1)) Underneath the blue "GeoNet" bar atop this page is the magnifying glass thru which to search across GeoNet. In this case, searching on the two words "compare scene", I got this result:
((2)) If ever you don't find the needed result, ask an actual audience (people), as happened here, but be sure always to ask questions in the best place. The T3G group has only ~350 and is a private group, with discussions invisible to the rest of the community. We're all nice, but we don't know everything, and often miss posts. Something like this should go to a wider audience, such as to the ArcGIS Online space.
So I clicked on the link you provided above, and got this as a search result, which I didn't find very helpful.
Earlier, when I saw Bob's posting I had done a web search for the compare template (I think he was looking to compare maps, not scenes) and found this link
https://www.arcgis.com/home/item.html?id=87ac24135d5341b39b871ff02f3afe49 which indicated that the Compare App had been in "mature support" so I'm guessing has now gone away. Even the linked sample app now only opens with one map.
I chose to reply to Bob personally, because was hoping that someone else had more info and would respond to his post. It's sad...I thought that the compare template had some advantages when you wanted to compare more then two maps so couldn't use the swipe app.