I had an embarrassing moment with this at an age where most people know the score regarding this (NT people I guess, that is).
I was in my 30s before someone actually told me for the first time "You don't have to answer with real details about how you actually are....nobody who says that actually wants to literally know, ya know" and laughed at me. I was so embarrassed. I'd gone through more than thirty years thinking the greeting "How are you" and "how you doing?" was a real question and I'd always given a real answer.
When this person finally said basically that he didn't even want to KNOW how I really am, it felt awful, and I started rethinking everything about that greeting and all the responses I'd ever given it.
It was something I had to actually
be told and/or learn mechanically, that when people say things like that, it's nothing more than a greeting, not a question. But even though I know that now, it still seems frustrating and weird to me. I go along with it to fit in but it still seems like a confusing convention, to me -- because every once in a while it CAN be a real question asked by someone actually seeking the news....
I had someone give me this exact same advice, but I was younger at the time. I think I was in college.
The problem is now I will ask people the same question and want a real answer, but they think I am just making a polite greeting.