Hey @Steve_Nicolai, thanks for this detail! I hadn’t considered the possibility that the app had somehow become corrupted, in part because the dialog is so matter of fact about how the developer needs to update it and in part because several other apps were affected.
However, you were spot on—when I deleted the Momento Classic app and reinstalled it, it opened up fine. This alone wouldn’t quite have solved my problem because deleting the app also deleted its data, and when I reinstalled it, its data was gone. But now I believe I could have restored the data through iPhone Backup Extractor.
I confirmed your technique by deleting and reinstalling Photo Studio, another app that was showing the same problem. Complete success, though if the app had any data (I never really used it, so I don’t know), it would have been lost too.
What this suggests, however, and I can test this later, is that erasing the iPhone that’s having the problem and restoring from a backup might fix the problem purely from the standpoint of reloading the app from the App Store during restore. I’ve found another app on my iPhone 11 Pro that’s showing the problem (NME Daily), so once I have the time later today, I’ll backup, erase, and restore. I think this will work in part because all the apps I’ve had trouble with in this way work on my iPhone 7, which was restored from the iPhone 11 Pro backup.
I do believe this will be contingent on the app still being in the App Store in some way. I don’t quite know what drives this, but some ancient apps are, whereas others are not.