How to get data from an app that is no longer available on iPhone?

dimitra147 wrote:

I need to retrieve data of the app that is no longer available in app store.

Maybe you could provide an email of the developer, so I could ask for a file with my data.

We’re not Apple, the people that work for Apple may or may not read postings around here, and Apple are unlikely to provide any contact info for an app developer. You’re likely limited to what the app developer has previously provided directly.

Your best option is to locate and contact the app developer and to potentially offer to pay them for their assistance.

More effort is to find and reverse-engineer the data in the app from a backup or similar archive, where that reverse-engineering is permissible.

This where such reverse-engineering is permissible:

• https://www.nowsecure.com/blog/2021/09/08/basics-of-reverse-engineering-ios-mobile-apps/

You’ll need a copy of the app for that approach to work.

Alternatively, and where permissible, you’ll be reverse-engineering the app data storage for its contents. This assumes that the data was not encrypted, as that only adds to the complications involved here.

If older versions of the app are still available in the app store, then acquiring an iPhone 6 might be useful for downloading the old app, and then accessing iCloud data. If the app has been entirely removed, this approach won;t be feasible.

Other folks may well already be reversing the app, too

If an app is no longer available in the App Store, then the developer has abandoned the app or the whole of the Apple App Stores, or they did something seriously bad to get kicked off from the App Store.

Their contact information may have changed since. Or they may not wish to communicate with former app users, as they may not see you as a client anymore. At best you can try a web search.

Hard lesson: don’t store information in apps as the only copy. Ever. If an app has no export mechanism, then that may be a red flag for some apps. Especially vault apps or password managers.

You haven't specified which third party app