Hey Miker2340,
Please see if the steps below may help with your iPhone 13 Pro Max and this Bluetooth audio issue:
"Connect using Bluetooth
- Restart your device.
- Go to Settings > Bluetooth, and turn off Bluetooth. Wait for about 5 seconds, then turn Bluetooth back on.
- Check the manual that came with your car for more information on how to pair with a Bluetooth device. Most cars require a phone setup on the car display.
- If you've connected multiple phones to your car stereo, try renaming your device: Go to Settings > General > About > Name, and type a new name. Then try connecting again.
- Update your device.
- Make sure that your stereo is using the latest firmware from the car manufacturer. Check your car's manual for more information.
If you still can't connect, contact Apple Support."
Those steps are from this article: How to connect your iPhone, iPad, or iPod touch to your car - Apple Support Your iPhone may still connect for Bluetooth calls, but could possibly help with your Bluetooth audio issue when trying to play music.
Take care.