This is predicated on overly optimistic population predictions by the UN. The CBO predicts peak US population in 2056, the US Census in 2080, for example. The UN is notorious for overestimating forward looking fertility rates or potential rebounds from current lows.

https://www.billkingblog.com/blog/the-u-n-has-quietly-lowere...

https://www.aei.org/commentary/peak-american/

https://ourworldindata.org/data-insights/fertility-rates-acr...

https://usafacts.org/articles/what-will-americas-population-...

https://www.cbo.gov/publication/61879

(fertility rates are converging globally at ~1-1.6 TFR, with some countries as low as 0.6-0.8)