The new feature hasn't been released to Google Play Store yet, but you can exercise it in Android Studio at the moment.
Start here with the Custom Sharing feature documentation in the Fedilab app at:
which shows you how to test against a sample site, e.g. teci.world
Then, you can look at the content creation management system that Tom created today, that uses the Custom Sharing feature, with more features and security, at:
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!