Just a couple of hours ago, my girlfriend set the hearing aid function up for her father. He apparently has severe and profound hearing loss, so all Apple would do is refer him to an audiologist.
So, my girlfriend cheated the test a bit by taking the test herself with his Airpods Pro. She got the test to diagnose him with hearing loss, but not so much that the hearing aid function wouldn't kick in.
The result was that he was absolutely thrilled with the results, with increased hearing ability. He was one happy man!