Playing .mp3 files on car audio from a USB
I no longer have a CD player so have imported a lot of my music from my CDs into Music on my Mac, using the settings to ensure the files are mp3s. I have transferred some of those files (as a test) onto a USB drive. However they appear to require the Music app to play. How do I get them to play in the car, please, as I am getting an error on my car's audio system 'Unsupported' and nothing plays (as I have formatted the USB correctly this is not because the file system is incompatible...)?
Mac Pro (2019)