A sample app which demonstrates how to hide sensitive information in an iOS app's snapshot image in the App Switcher. This version is for Swift. There is also an Objective-C Version.
See my Medium article Hide Sensitive Information in the iOS App Switcher Snapshot Image for details on how the technique works.
A pre-ios-13-support branch has extra code which and extends the solution to work prior to iOS 13 where the App Delegate is responsible for showing the privacy protection window.