Receiver
If you buy a “kit car” that is listed as “needs a receiver,” then you don't need to buy a receiver.
The Jetson Nano and the PWM/Servo driver will replace the receiver, outputting control signals to the car. If you’re buying a kit with a steering servo, motor, and ESC, you should actually try to not get a receiver, since the RC car could be specifically designed for that receivers PWM signals, and you’ll be taking it apart anyways.