Using USB to play music in your vehicle

Might need to check the car documentation on how to pair it with an iOS device. I think the car believes the iPhone is a Flash drive or something and it most definitely is not. Also will need to tell the iPhone to recognize the car and grant access to the music it contains.

If I plug my iPhone 11 Pro into the USB for my 2015 Mercedes-Benz C300, it will appear as an iPod, and I can play music all day long. No problems at all. Doesn't look for a Fat anything, just the music on the iPhone. If I don't wish to plug it in, I can pair it with Bluetooth and play the music that way too.

Oh, but you can. Provided the car and the phone agree. My iPhone 8+ happily plays all its tunes on my Mom's Fusion with MS Sync thru the car's USB port. Just had to tell the car to recognize the phone and the phone to allow the car to talk to it, as detailed in the car's Sync manual. No CarPlay configuration needed. You even get to choose which songs are playing, with the name up on the car's info window, all controlled with the steering wheel controls and the phone safely tucked away in the seat console box, where the USB connector is located. And the phone gets charged, as a fringe benefit.

Exactly. Dunno how Mercedes calls theirs, but Ford had a partnership with Microsoft, which created for them the Sync (TM) product powering their in-car entertainment system. The phones indeed, register as iPods and allow the Sync code to access all the musical content. This is what the OP is trying to get done and is occurring partway, since the screen has already identified the device as "Alfred's iPhone" so my guess is that the phone needs somehow to grant access permissions, but I could be wrong.

What car make, model, year are we talking about, anth_pero?

You can't play music that way. When you plug a device into USB, it's looking file a file system like FAT32 or exFAT with MP3 files on it such as a thumb drive would be. Since you phone doesn't show up as a drive like that, this is why you are getting the message.

You will need to either use Bluetooth or Apple CarPlay to play music from your phone

It appears that Ford has a special sync feature that will allow you to connect your phone, not all car audio systems have this.

I stand corrected. Some audio systems are able to play music from phones.

Not all systems are capable of this as I suspect is the issue with the OP's audio system.