Abysmal sound quality.
Low volume. No bass or treble. Plus, snap/crackle/pop intermittently during any audio playback; Apple Music, SiriusXM, Audiobooks, Podcasts, etc.
Two phones. 7 Plus and 6 Plus, both running 12.3.
Reset Network Settings, Rebooted Phone, no changes.
All Apple-branded cables; tried multiple cables, no changes.
Two (2) different vehicles: 2018 GMC Terrain (Bose Premium) and 2019 Subaru Forester (H/K Premium).
Same problem.
The only workaround is to either use the phone on Bluetooth (no USB) or turn-off CarPlay altogether and use it (literally) as an iPod via USB.