I wasn't surprise when I saw that in the comments sections there are times when people reply to others with @username to mark it, but I'm being wondering if that's a real thing (the person in question receives a notification or some alert of some kind) or it's just a mark to say to readers that you are not talking to yourself but to another person.

I encountered some comments that asked for feedback that are a couple of years old (even a decade) and I was wondering if I reply I would be shouting to the void or the other user would know that I responded to them.