A:Answer The USB dongle is hardware/software combo. When the USB bluetooth dongle is plugged into a computer, the computer reads the device ID, identifies what type of device it is then loads the appropriate driver/control software to make the hardware work correctly (then stores that info in the registry, if you're using Windows). Modern OS should be able to recognize the USB bluetooth dongle (assuming the OS has the functionality to recognize newly added hardware and deal with it appropriately). As an example if you were to plug the bluetooth dongle into a WIndows 10 computer, the OS will auto-recognize the the device then load the appropriate drivers so that the OS knows how to control the device and allow you to interact with it such as adding a device to the bluetooth to send/receive data. If you were to plug the same bluetooth dongle into a really old computer (such as that running Windows 95) you'll get an error or unknown device message.
Most likely your car's aux USB isn't set up to auto-recognize USB hardware other than 'generic external storage device'. Unless your car's audio system has control function to access external USB bluetooth device AND be able to load the appropriate drivers for the particular device it won't work. Keep in mind that even if your car's aux port recognizes the USB device you'll need to be able to access it via radio/system control so you can link your phone/computer/tablet.... etc to the bluetooth so you can send data (stream music/Android Auto/Apple CarPlay).
