This, in my experience, is very common in English-speaking countries as a polite/formal phrase between strangers where the answer is usually "fine, and you?" or a version of that.

It was what shocked me when I went to the US because I perceived it as very rude (looking back I find it amusing). I'm not sure if all of Eastern Europe is like this, but usually in Romania you would never ask a stranger how they are, because the question is quite personal. In other words, when I ask someone how they are, I expect them to actually tell me about their life, how they doing, etc. It would be like sticking my nose in other people's business by asking a complete stranger that. At least that was my initial perception of it at the beginning.

My response now is usually "Fine, thanks."

Good reply, never a need to be rude

Interesting topic that I've thought about often. Bottom line is, I'm a truth-teller. So I'm usually mindful of an honest answer and, if possible, delivered with a positive attitude. In the last 15 months while recovering from back surgery, I often say, "Great. I'm happy to say I can walk again. Although not very well yet."

This is a polite courtesy that I have always wondered about. I think people ask to be polite and sometimes out of habit, but most don't want to know.
I usually smile and say "I am fantastic!" Pass along some cheer.
However, I do wonder what they would do if you replied, "I'm terrible. I have this rash on my..." It crosses my mind when the cashier is especially dull or rude.

If it's a stranger, like a cashier I don't know, I usually respond with "really great". If they ask, "why are you so great," I'll respond with a smile, "because I woke up". That normally leads to a pleasant interaction. If it's family or friends I'll tell them more detail but it won't be much different to that.

While it may sound like a meaningless question our of politeness, in a small town like where I live it's a genuine question, a gauge of the health and well being of the customers they're standing 2 feet from, even though sometimes now behind plexiglass.

I take it as a opportunity to gauge my own happiness, which at this time is positive, and a reminder to smile and say something positive. I sometimes forget to check in with my own well being, which currently is great!

In a small community where we all feel a connection to each other, and the social distancing has affected many with depression, it's good to ask and gauge the mental health and wellness of the customers. I appreciate the question.

When I was recovering from my mystery illness (6+ months ago, before testing, masks, common quarantine and sanitizer protocols) I took the question as an opportunity to warn the cashier (and customers standing too close to me in line) that I was still trying to kick a horrible mystery illness, though not hopefully not currently contagious. Folks would visibly step back. This is why I'm so glad that it's now common to social distance for health reasons. (I shouldn't have been out, but there were none of these contact-less delivery options that we now have.)

I'm so glad that now (6+ months after my recovery from what might have been covid) there is a variety of health safety measures such as contactless food/medicine delivery, masks, santitizer everywhere, social distancing spots, to help normalize the desire not to spread illness, as anyone could be a possible asymptomatic carrier.

Depending on who's asking and how lucky I feel, "I feel great. Wanna feel?"

I kid, I just said that to get the cheap laugh.

One of my favorite Jackson Browne lines:

Maybe people only ask you how you're doing
'Cause that's easier than letting on how little they could care

But he follows with a positive note:

But when you know that you've got a real friend somewhere
Suddenly all the others are so much easier to bear

To “How are you doing?” I reply either “Slowly” or “As slowly as I can.”
To “How are you?” I reply “I’m doing well for an old goat.” To pals I may say “...for an old fart.”

I’m retired and at 89 can say anything I like.

Ask them how they are doing, during the first month, I saw a lot of scared eyes above masks, I would stand away from them, make eye contact, say hello, thank you, how ya doing, etc. Also, they are trained to let the customer, go before them, even if they have a huge load to pull, I started insisting on letting them go first, because I've do reshelving, and know how heavy those carts are.

Why do you want to know ?

I quite often answer I am doing great nobody has screwed the day up for me yet , How about you ,they usually chuckle

I generally try to respond with something upbeat like I'm finer n frogs hair today, or wonderful I've got me a pasel of deim to start commencing to carpe. In general something stupid to get a laugh.

I use the Russian нормально or как обычно for japery.
They both mean as always, the same. It usually gets attention.

"Pretty good. How you doin'?"

My history of this is to say, "How are you?" and I usually get a string of actions they are trying to do. So I ask again and the person usually looks at me and says, "What?"

"They don’t actually want to know. Not really. It’s just a polite, meaningless question. They want a polite, meaningless answer like, "Fine, thanks.""

I don't know who you've been having out with but when one of my friends calls me, or I call them, the question isn't phoney at all.. We talk..

I tend to say I'm doing better than average, I lie like that.

"Fine. And you?" Tit for tat, britches.

You’re response is accurate and also positive. Most people really don’t want to know the depths of what you are feeling. They just want an upbeat answer with no real content. Your close friends might ask again, “but how are you really doing?” They want to understand you.

My nearby town only has about 350 people. There are no complete strangers. Responses there are much more involved than if off in the city.

"They killin' me".
"They" being the angel of death and cronies.

"Well."

Which is true.

I've been answering "I'm OK".