I purchased this USB-C / USB-A drive from Amazon. Downloaded music and plugged it into the USB-C port in the car and recognized instantly. Worked great.
https://www.amazon.com/dp/B0BD72M6Y4?psc=1&ref=ppx_yo2ov_dt_b_product_details
Not a Mac user, but Windows and having same issue. Formatted Fat32, went to the USB icon and then inserted the flash drive and getting error. Brand new flash drive, so speed not an issue.
???