Hi ariell26,
As wired CarPlay and wireless Bluetooth are different connections, it seems you're describing two unrelated concerns.
Regarding the behavior with Bluetooth, that sounds like what is described in Headphone notifications on your iPhone, iPod touch, or Apple Watch:
"After receiving a notification, the next time you plug in your headphones or connect them via Bluetooth, your volume will be automatically set to a lower level. You can still turn your volume back up if you choose."
If you live in an area where this feature can be disabled (it is not possible in all locations), then try the following including the Reduce Loud Sounds setting:
"Turn headphone notifications on or off
- Open the Settings app on your iPhone or iPod touch.
- Tap Sounds & Haptics, then tap Headphone Safety.
- Turn Headphone Notifications on or off.
You can also turn on Reduce Loud Sounds to automatically lower your headphone volume when it exceeds your set decibel level."
Regarding CarPlay, the page If you need help with CarPlay offers the best steps:
- "Check your connection to your CarPlay stereo:
- If you have a wired connection, try connecting again with a different USB cable to a different USB port if you have one.
- If you have a wireless connection, make sure that Bluetooth is turned on on your iPhone under Settings > Bluetooth. Then go to Settings > Wi-Fi, and make sure that Wi-Fi is also turned on. Tap the CarPlay network, and check that Auto-Join is turned on.
2.If CarPlay doesn't activate automatically, look for the CarPlay logo on your car's display and select it.
3.Restart your iPhone and your car.
4.Make sure that Siri is on.
5.If your iPhone isn't detected by CarPlay, make sure that CarPlay isn't restricted. Go to Settings > Screen Time > Content & Privacy Restrictions. If Content & Privacy Restrictions is on, tap Allowed Apps, and make sure that CarPlay is enabled.
6.Go to Settings > General > CarPlay, tap your car, then tap Forget This Car. Then set up CarPlay again.
7. Make sure that your CarPlay stereo is using the latest firmware from the car manufacturer. Check your car's manual for more information.
If you still have issues connecting to CarPlay, contact Apple Support."
Regards.