Physical system volume button press notification on iOS 15?

Physical volume button pressed notification "AVSystemController_SystemVolumeDidChangeNotification" stopped working with the release of iOS 15.

1. AVAudioSession::OutputVolume (https://developer.apple.com/documentation/avfaudio/avaudiosession/1616533-outputvolume?language=objc) seems like the preferred approach but the limitation is that it doesn't provide a callback when volume is at max (press up) or min (press down). is there any alternative to get the callback even when the volume is at max or min?

2. There is a new notification available "SystemVolumeDidChange" that works similar to "AVSystemController_SystemVolumeDidChangeNotification". Please can you confirm if it a Private API or if it may be used to publish apps on App Store?

3. Our use case requires the physical volume button press notification even if volume is already at max or min. is there any other alternative approach available?