You probably could but then you would have a crippled iPhone.
Assuming the 18.1 versions all over the world include all of the Hearing Aid features and are just switched on an off according to location.
I'm thinking out loud here. Maybe you could set your iPhone to the US or some other country that allows the update and switch location off? Would it cease working if you then changed the location to the UK? I don't know. Maybe you will simply have to leave the country set on the US. In the end, I wonder if it is as simple as that.
I also don't plan on trying it on my iPhone until I am 100% sure it will work and I am in no hurry. A new IOS always has bugs that settle down after the first few versions. Especially other apps that I rely on.
I don't consider the 18.1 update crucial at all. The Airpods are already working for me as hearing aids running 17.7 and I was updated yesterday night to the new firmware. I haven’t noticed any changes since the update.
Having said all that I would love to try the new AI features etc but can’t if 18.1 is going to break my hearing aids.
I was hearing on another forum that a Canadian went over to the US to update and went back.
The question is does the Hearing Aid function revert and "switch off" if you have to do something simple like a restart.
I wonder if Apple have left the lock quite easy to workaround as they want as many people as possible trying their "new" Airpod hearing aids.
