There are many Bluetooth to AUX adapters on the market such as the TaoTronics TT-BA07:
Having an option for Aux to Bluetooth would offer much better sound than Aux to FM. The Tesla Model 3 even allows this module to be paired as a Bluetooth device, however it pairs incorrectly. When the device is in Transmit (TX) mode the Tesla doesn't see it at all. When the device is in Receive (RX) mode the Tesla both sees it and pairs with it, but this is the opposite of what is needed. The car should not be sending sound to the module, the module should be sending sound to the car.
This forum post contains additional information about the issue as well as some troubleshooting that's been performed: