My wife’s phone has encountered this issue with her upgrade to iOS 18 (non-beta). Mucis acts as if it’s in a phone call (volume cant be turned all the way down and only front speakers pipe music): the phone‘s volume doesn’t show the standard CarPlay icon; and at times music only plays out of the phone whilst controlling play/pause on the car. As some here reported, playing on the phone sometimes resolves on its own after a few minutes of it being connected. it seems that the audio handoff to CarPlay isn’t happening or when it happens it’s identifying it incorrectly as a phone call/notification. 2019 Chevy Traverse, iPhone 15