There is no way to turn this off. Clearly, thousands of people have been trying unsuccessfully, many of which have contacted Apple directly. It is not a glitch or malfunction. They have no intention of changing it.
It’s a shame because it severely limits one of the primary functions of an iPhone for many users, an audio media delivery device. And let’s face it, any threat to Apple to switch companies or devices will fall on deaf ears. 1) Why would that care about a few people’s business vs. complying with gov’t regulations, and 2) they know it’s an empty threat and we wouldn’t actually do it anyway.
However, I do think it is very reasonable for us to request that they find a way to differentiate between different types of Bluetooth devices (assuming that is technically possible). This restriction should not apply to audio devices that have a secondary volume control. Most of these devices depend on full volume being delivered from the phone in order to produce the expected volume at the speaker.
For example, my wife is the Assistant Principal at a Middle School and they play music in the car-rider drop-off line in the mornings. They use an iPhone and a Bluetooth speaker to do this. But with this new feature, after 15 minutes at full volume it cuts back 50% and they cannot get enough volume out of the speaker for it to be heard. Our family has the same issue with the Bluetooth speaker we use outside in the backyard, and I also have the same issue now with the Bluetooth FM Transmitter I use in the car for music and podcasts.
Though I don’t think it likely, I do wish Apple would listen to their customers on this and improve the feature so it does not have such a broad-brush application to all audio content.