The birth rate has declined in every country as that country has developed a modern economy.
Only parts of Africa and a few muslim countries have what would be considered a high birth rate today and even those are falling every year. Saudi Arabia, for example, is down to 4 children per woman versus 7 just a decade ago.
The world population is estimate to peak out at 8.6 billion (not 10) which is not much higher than today’s 6.6 billion.
Is that true? Can you cite your sources?