Of all the potential problems facing our species, running out of new people does not seem to be a concern at all. I’m not surprised that during a worldwide pandemic, our birthrate fell in a society marked by ready access to effective contraception. I don’t think it’s reasonable to draw a straight line through that and worry about declining population, but I suspect this was written to be read about as reasonably as “…
See, for instance, this post on the upcoming issues for China due to demographic difficulties: https://zeihan.com/the-end-of-the-last-best-chance/
It takes 20 years to make a 20 year old, and economies, especially those like the USA where consumer spending drives most of GDP, need to adjust if there's changes in birth rates. We did it one way with the boomers, will have to do it again in a different way if there's a bust.