I’m American, and I’ve known enough couples that opted out that I usually ask “Do y’all know if it’s a boy or girl?”. It’s less common, but I bet 10-15% of couples opt not to know. More for the first baby (with later babies, there’s practical reasons to want to know earlier).
It’s pretty uncommon these days. A friend of a friend just had a baby and opted not to know in advance. That’s the only person I know of who didn’t find out before in the past five years.