>It's true in East Asia as well.

No it isn't.

>In fact, where is it not true?

Everywhere? Nothing in your link contradicts what I said already. You can only make the correlation if you cherry pick start and end dates, and cherry pick western nations or nations that had coincidental birth rate declines like China. If the correlation is real and not spurious, then why doesn't it hold now? Why didn't it hold before the 1930s? Why has it never existed in Africa?

How is it not true in East Asia? The rich countries (Japan, South Korea) have super low fertility rates; the poor ones have higher (North Korea). Can you point out some clear violators?

The inverse relationship is obvious in South Korea:

https://tradingeconomics.com/south-korea/gdp-per-capita

https://fred.stlouisfed.org/series/SPDYNTFRTINKOR

Before the 1930s, every country was "developing" my modern definitions. (US real GDP/capita was ~$9k in 1929 just before the recession). Also, other factors are necessary for this to happen (e.g. women empowerment)