In British English it is a fairly recent innovation. I personally would answer "well". Under influence from America, I think younger people tend more and more to reply with "good". It seems wrong to me but usage changes.
– chasly - supports MonicaMar 05 '21 at 02:28
A (partial) answer to this question is buried in the linked duplicate, perhaps it's better to write it as its own separate answer here.
– GlorfindelMar 05 '21 at 12:53
I usually respond “I’m doing well, how are you?” I sometimes respond “Can’t complain, how about you?” Or “Fantastic! How are you?” Or “I’ve been better. You?” or many other ways depending on how I’m feeling and who I’m talking to.
– ColleenVMar 05 '21 at 13:22