Aux cord not working

I see lots of questions on here regarding the inability to play music using an aux cord in an older car since the 16 upgrade. It’s ricudulous that every Apple response is blaming cords and car ports/stereos. It’s clearly the upgrade. I’ve already spend an hour with Apple Support. I wish there was a way to undo the upgrade. Paying for iTunes and not being able to listen in the car is pretty torturous. I don’t have a USB port in my 2009 vehicle, just the 1/8 aux cord port. If anyone has any ideas, please let me know. It’s not my equipment, if that wasn’t clear.