We will be releasing an update soon to address the changes need to make App Inventor apps compatible with Android 12. The update is available on the test server at http://ai2-test.appinventor.mit.edu.ezproxy.canberra.edu.au/. You should test your extensions both in the companion and compiled apps on the test server to ensure your extensions work with Android 12.
One major point is that if you are declaring activities, broadcast receivers, or services, you must assert whether those items are exported or not. Previously, Android assumed that these items were exported if the appropriate information was not provided. However, it may not make sense to export these items and so you should consider whether it makes sense to set the exported field to true/false based on the needs of your extension.
Any extensions that use those entities but do not update to explicitly indicate whether they are exported will fail to install on Android 12+ starting with the next major release of App Inventor.
Another point is the Pending intent mutability: You must specify the mutability of each PendingIntent object that your app creates, i.e. you have to specify FLAG_ IMMUTABLE or FLAG_MUTABLE. See for example this extension
The actual Users of Extensions are unlikely to see your post Anke because Extension Development is a sub-category and thus not listed in the Forums drop-down of categories.
