China has a very small and narrow window when it is at its peak. Then, the numbers very quickly turn against it. You have not mentioned rising sea levels on the coast and mass internal migration caused by global warming. Birthrates are now collapsing all over China; this is an early indicator that prospective parents are not confident about the future.

I believe that we will see a major global population collapse in this century, starting in the 2040s, with population falling from 7.2B to 3B by the end of the century.

China will turn inward, and will largely shut itself off from the rest of the world, just as it was before the early 19th century.