If the source data (world/map data) is untouched (silly example - the trashcan in the corner), then it's the front-end that has changed, aka the app version filters things differently in this new version and gives preference to "setA" data (e.g. banks) vs "setB,C,D" data (e.g. trashcans, burger places, trashcans, benches).
Then "all" we have to do is fork the front end and keep it steady (with the assumption that the API is open and it will allow 'foreign' apps accessing their data - for free), or stay on the same non-updating app forever. As a principle I don't update apps, unless I absolutely need to (app nags to update 'or else').
I'm not a dev, but without having to rebuild the universe, I don't see any other solution that does not take massive effort.
Also, Ondřej Sojka speaks on the interface. How about the many GB/TB required? Is the new company willing to freely hand out an API that will provide thousands of hits, for free? Are they that generous to pay for the storage, network for someone else's charity?
ADDITION: just because I know this area (of the map used) pretty well, if you are ever there, try the "Honest Burger". I hope they survived the COVID shutdown.. they make what I call honest burger (I use this term for everything of a fair price/value)(way before I discovered that place). I especially liked the fries with rosemary. You don't get that often in a burger palce.