

WestNordOst seems to be the user name of the main developer.
How exactly is the data used, does it go back to openstreetmaps?
I can give you one example. If you go to a bench and answer the question “Is it still there” with “yes”, the bench object tracked by OpenStreetMaps will get a tag that is similar to “last-checked-for-existance: 03/16/2025”. If you answer “no”, it might get removed from the OSM database. So, yes, it results in changes in the OpenStreetMap database.
Tethered to commercial Jawg.io for map tiles
Not sure, what that means, sorry.
I have also linked the FAQ (which are by the way hosted by OpenStreetMap) ->https://wiki.openstreetmap.org/wiki/StreetComplete/FAQ#How_does_the_app_handle_uploads?
Me neither. Unfortunately not open source…