A huge number of women have just hit 40-years-old, so they can not longer have children. The one-child policy means there are hardly any children, AND female children were aborted to have a male child, so there is something like 125 males for every female, which exacerbates the problem.
China is far from the cheapest place to manufacture anymore and companies are flyuing out of China because of that and belligerence and supply chains and opaque laws, mandatory technical transfer, and so much more. All this is making land and housing expensive, and poor paying jobs so that they young cannot afford stuff, which is why "laying flat" is such a big deal there now. Why work hard for nothing, no chance of making it?
Same with Russia, for a long time, and this war has killed how many young Russian men in the prime of their life, and also to flee the country, most likely permanently in many cases as they find jobs and settle down in new countries.
Russia and China are in serious trouble demographically. This is why Russia attacked Ukraine, in my opinion. They will even have less manpower in 10 years. And I think this is going to drive China to attack Taiwan - they just won't have the manpower in 10 years, not like they have now...even with 1 billion people.