Hello Naosis,
Thanks for reaching out and providing all the details here in Apple Support Communities. Based on your post it sounds like you're having trouble playing Music in your vehicle using CarPlay. Is that right?
Does this seem to occur with multiple audio related apps?
Can you play content using Music on the iPhone without being connected to the vehicle as expected?
Are all the different cables in use Apple certified? Have you tried testing using shorter cables?
Identify counterfeit or uncertified Lightning connector accessories
Also, take a look at the steps listed below. You can also try reinstalling the Music app since this seems to occur with content downloaded to the device as well. Keep in mind you'll have to redownload the content back to the device once Music is reinstalled. If you continue to run into complications, you can reach out to Apple Support directly.
If you need help with CarPlay
Delete built-in Apple apps on your iOS 12, iOS 13, or iPadOS device or Apple Watch
Get Support
Warm regards.