iOS 11 brings a number of enhancements and new features to your iPhone and iPad. In this new update Apple has switched from 32 bit apps to 64 bit apps. If one or more of your apps have not been updated for the new system, it won’t work with iOS 11. Here’s how to tell which apps won’t work with iOS 11.
Go to Settings > General > About
Look for Applications in the list that appears.
You’ll get the App Compatibility screen and see a list of apps under the heading “No Updates Available”
Note you do not need to be running iOS 11 to see this list. In fact, I recommend you wait a few weeks before upgrading. Minor bugs often appear when a new operating system goes public and millions more begin using it. Wait a few weeks so Apple can fix the small flaws missed in the pre-release versions.