Hello. The answer to your question lies in the comment line of this snippet:

class MyWorkManagerInitializer : DummyContentProvider() {
    override fun onCreate(): Boolean {
        WorkManager.initialize(context!!, Configuration.Builder().build())
        //run your tasks here
        return true
    }
}

As you noticed, this class is almost same as WorkManagerInitializer exept, that in your own class you can run our application specific tasks. In WorkManagerInitializer you can not do that:

So our MyWorkManagerInitializer looks pretty similar to WorkManagerInitializer. Moreover it expands WorkManagerInitializer with initialization of required tasks, but we can not just extend WorkManagerInitializer since it has restricted access