I’ve seen the “how are you” questions on this forum, but mine is a bit different.
I read this in the Readers Digest once:
Don’t tell your friends about your indigestion. ‘How are you’ is a
greeting; not a question.
So if it’s a greeting, should it be
How are you!
How are you?
How are you.
I wouldn’t rely on the ‘Reader’s Digest’ for information about English. How are you? is indubitably a question, and so requires a question mark. The fact that the speaker doesn’t expect a detailed health bulletin in response is beside the point.