How to build and distribute the app

Android

In Android Studio, go to "Build">"Flutter">"Build App Bundle".
Then drag the created .aab file into the Google Play Dashboard (Create new internal release).

In the terminal, run flutter build ipa (takes ages)
Open the build/ios/archive/MyApp.archive with XCode
First "Validate App", then "Distribute App" to send it to testflight
In the AppStoreConnect, in tab "TestFlight", wait for the version to become "Ready to submit"
In tab "Distribution", create new release (+ button on the top left) and add the build version