The only thing that worked
The only thing that worked for our 2018 RAM with a Genie garage door opener was the following:
Clear out anything previously programmed into the in-car system from the factory by holding down on the 2-outside buttons simultaneously, until the in-car LED starts flashing rapidly. This may take up to a minute (in most cases, the key should be on auxilary, and/or the car door must be shut).
Decide which button you want to make to be your in-car garage door transmitter. Hold your transmitter up near the selected button, pressing both the garage door remote and the selected in-car transmitter button simultaneously. Hold down on the buttons until the in-car, LED light flashes rapidly. This sets the in-car remote transmitter to be your garage door openers make transmitter, but you are not done. You now need to make this in-car transmitter your personal transmitter.
Go to the Learn Button on your garage door opener. The button is usually next to the area where the floppy antenna is connected to the motor head. With Genie it is most often behind the light lens, and an indicator light flashes red when pressed. With Sears or Liftmaster (Chamberlain) it is near, or part of, the terminal screw board, and is a red, green or purple square button with a green, amber or purple indicator light. Press this learn button momentarily. The indicator light will turn on and blink if Genie or otherwise stay lit. For Genie systems, go back to the in-car transmitter button you programmed and press this button 3 or 4 times, or until the door starts moving. This should set your in-car transmitter to your garage door opener. For Liftmaster, Sears, or Linear Megacode press and hold the in-car button you programmed until the garage opener light flashes. Your in-car is now programmed to operate your door.