I have a 2019 BMW X2 with Carplay. The audio quality is noticeably worse with Carplay than through USB or even Bluetooth.
Carplay apparently transmits the audio via a wi-fi connection the phone makes with the car's head unit. It's higher bandwidth than Bluetooth, so Apple claims it can transmit lossless audio without recompression to the head unit. But it doesn't sound that way. (I watched a WWDC developer video from Apple that explained this)
I've played music through Tidal & Apple Music. They both sound the same through Carplay. Thin, lacks clarity. Doesn't really sound like mp3/aac compression though.
Does anyone know what codec/protocol is used to trasmit audio to the head unit? Anyone else experience this? I want to know whether this is a problem with Carplay or just the head unit's implementation of it.