It's not possible to use a rear door fitting bike carrier if you are using an electric tailgate. You would need to operate the tailgate manually with a bike rack fitted. Please consult the owners manual for your car to check if this is possible with your model.
If you are using a tow bar rack on a car with an electric tailgate it is also important you switch the tailgate to manual operation to prevent the tailgate from being opened accidentally with a rack on the tow bar.