I don’t think it’s a flex. It’s a major thing happening in their lives, so it comes up in conversations about what’s going on in life…
My wife and I will never have kids, but we know it’s a huge deal to those who do, and that once most people make the decision to try, it’s the most important thing on their mind and plan for their future. So yeah, if you ask someone who is spending 80% of their time preparing for a family “what’s up?” I think it is 1000% normal and valid for them to say trying and prepping for a baby.
As it isn’t an issue of bias or prejudice or personal harm, if someone is so squeamish and prude that they can’t let a friend (or hell, a nice stranger) give them a significant life update, they should get over it or pretend.
Oh of course, 100% agreed you can respond like that, and I’d chuckle and say thanks if it were me. Could also be a great way to bring levity to a situation that’s really difficult for some.
Also just want to add, I’m from Spain and it’s completely normal to say here. Definitely not an American thing.