Hi, Melbach.
Thank you for posting in the Apple Support Communities.
We understand that the system sounds have lowered significantly when using your Powerbeats Pro with your iPhone after updating the iOS software. Having your messages read aloud when you have your Powerbeats Pro connected is one of our favorite new features, and we’d be delighted to see if we can help get your settings back to an audible level.
Are you able to adjust the volume on your Powerbeats Pro as the message is being played? Your iPhone has different volume profiles (e.g. system, media, etc.) and the easiest way to manage the volume is to adjust it as that specific feature is playing.
If you’re not able to adjust the volume, try checking to see if resetting your Powerbeats helps.
Reset your Beats earphones - Apple Support
Your Powerbeats Pro firmware should remain updated when connected to your iPhone, but it may we worth manually checking to see if they need an update.
Update the firmware of your Beats product - Apple Support
Respectfully.