How they work
You create an event in App Store Connect with a name, short description, image or video, start and end date and event type (challenge, competition, live event, major update, new season, premiere, special event). Event cards appear on your product page, in search results and can be picked for editorial featuring.
Events are discoverable to people who don't have the app yet, and remind existing users to come back — helping retention.
Google Play equivalent
Google Play calls it promotional content (formerly LiveOps): events, offers and major updates shown in the Play Store.
Example
A running app creates a "30-day spring challenge" event. The card appears in search for "running challenge", brings in new users and pulls lapsed users back for a month.