I live in India and I have been using hearing aid feature since at least March when I bought Airpods Pro. Only that it wasn’t called as such earlier. It uses the audiogram I had provided it which it used to create a customized equalizer for my hearing disability. I am sure they must have improved upon the capability in new OS versions but functionally it has been present for a while now.
I suppose the difference is 1st party support for creating the audiogram, plus the clearance from the US gov to market it the way they want as OTC hearing aids