I managed to make the keyboard extension re-appear by switching the affected apps' language back and forth. For example if your preferred app language is English, then you can go to Settings > (the affected app) > Preferred Language > switch to another language > launch the app > go to settings again > switch the language back to English.
GordonWKC
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My solution:
Create screenshots with iPhone SE simulator with iOS 17.
Download iPhone 8 Plus simulator with iOS 16.4
Drag the screenshots into the iPhone 8 Plus simulator.
Open the screenshots with Photos app in the simulator.
Screenshot the screenshots.