Is there a way to visit the mapbox-map created in the app by a URL?
I don’t believe so. It appears the map is simply averaging the locations from the spreadsheet and the pins are just dynamic overlays. The URL is simply referencing a centralized lag long from the average I think.
For example the City Guide template references this map, which is just a map of the centralized pins:
https://apps.mapbox.com/feedback/map/#13.79/37.77116/-122.42317