My secret calculator won’t work after update. I paid the annual fee but still not working

Check for app updates, check for iOS updates, and then check with the app vendor.

An iPhone X can run iOS 16.6, the current version. You’re about four years back with your iOS, here…

The availability of some of these “hidden” apps and third-party password apps can sometimes vaporize on little or no notice unfortunately, and recovering data from within the app can be a project. Particularly if the app was written with data security in its design. If the app was just storing stuff without much regard to data security, recovering the data is still a project, but can be somewhat easier.

… Contact a third-party vendor - Apple Support

… Update your iPhone or iPad - Apple Support