If you have an older iDevice with an older versions of whatever app you can no longer access on iOS11, already on the older iDevice, you maybe able to retrieve the data that way. The older app already needs to be installed on the older iDevice and already being used on the older iDevice.
Other than this possibility, no other hacks or procedures will work to retrieve the data from an iOS 11unsupported app.
There are no possibilities.
Discontinued/unsupported/abandoned apps are still the property of its original developer/s/owner/s.
If ANYONE tries to reverse engineer an existing app, without trying to get expressed wriiten, legal consent of the software app developer, this could be legally considerd as software copyright/patent infringement and the original developer/s have every right to sue such patent/copyright infringers trying to recreate someone else's software apps, in an attempt to retrieve their app data from their no longer supported or abandoned app.
There is nothing, NOTHING, any user can do if an app developer has gone out of business, abandoned app development of their app or decided to simply no longer keep up development of their app, any longer.
It's their software property to do whatever they want to do with it.
Software companies go out of business all the time for whatever reasons.
Some app developers are one or two individuals that simply decide to stop supporting and developing an app that they created, at some point, due to whatever reasons.
Apple assumes no responsibility to any third party app developers of their computing platforms.
