What's New is not just release-note housekeeping. It is visible on the product page and the Updates tab, so it can either increase trust or make the app look abandoned.
What Apple recommends
Apple says to communicate changes, especially features or fixes based on user feedback. List new features, content, or functionality in order of importance.
A good structure
- One short sentence for the headline change.
- Two or three bullets for meaningful fixes or improvements.
- No vague "bug fixes and improvements" unless that is all the release really contains.
Localization
If the update includes a localized screenshot refresh or a market launch, localize What's New too. A Japanese listing with English release notes reads unfinished even when the screenshots are correct.
Source notes
Apple's product page guidance describes where What's New appears and recommends ordering user-facing changes by importance.