I don't know. Perhaps because it is not necessary to have android:exported='true' declared for Android 11. Note Anke's " because
android:exported="true"
is not declared in the Manifest with the extensions used.
Any tip/hint if extension developers need to take care of this" in Androids lower than 12. "
It appears the third party developer's extension does not declare android:exported='true'.
MIT's older Companion might have provided the required manifest and the most recent Companion might not