Ya'll always need a boogeyman, trans people and DEI are the newest ones and happen to be the ones that seem to have truly stuck.
left-handedness used to be considered a mental illness until it wasn't. Once it wasn't the number of people who were left handed increased dramatically.
The oldest Gen Z'er would be around 27 or 28, the youngest would be 13. That age range alone would tell me more aren't having kids b/c they're too young to even consider having kids.
It's not really normal for someone between 13 to 20 to have kids. The average age of first time parents is between 26 and 27. So your theory as to why birthrates have gone down doesn't make any sense.
Added:
https://www.prb.org/resources/the-u-s-recession-and-the-birth-rate/