Anyway I haven't seen anything indicating this "new" hearing health stuff is anything more than just a new test app. For a long time now you could already use a third party hearing test app like Mimi, save the audiogram to Health and apply it to phone, music and transparency. It sure seems like Apple just wrote their own test app and hyped it to the moon.
I was hoping there would be an improvement in the custom transparency sound but nope, it still sounds like you live in a plastic tube when enabled. Oh well.