There has been much higher fertility during much worse times. They don’t really have much explanatory power on their own.
Like for example? With comparable ability to control pregnancy?
Historically people hold of kids during bad times - as much as they can
The U.S. birthrate hit historic lows during the Great Depression. It also dropped with the 2008 Recession and has never went up since.
Anecdotally I know only one couple who avoided having a second child because of climate crisis. They are pretty well off tho, have multiple long distance vacations per year and drive ICE vehicle /shrug.