Hi I'm not a overly technical person, and our app developer is currently on leave so trying to figure this out.
Our app was grandfathered a few years ago, but it's time to finally stop all uses having access to the app due to back end changes.
Is the only way to do this to Remove the app from App Connect?
What will the end user see? Do they just get a note saying the app is no longer functional?
As far as I know, removing an app from the App Store does not prevent users who have already installed the app from using it. It only prevents further downloads from the App Store, i.e. new installs or updates.
Also, it is against the App Store rules (again, as far as I know) to just publish an update that e.g. only shows a message that the app is not functioning anymore (since apps on the App Store need to be functional).
Since you mention a backend: could you just shut that off? Does your app handle that in any way and show a message?
Logically, users would receive an error message from your app if backend is off.
In any case, if you don't update the app for 3 years, it will be removed automatically.
May be the best is just to wait ?