China's already sitting on a ticking time bomb thanks to the one child policy. I'm willing to bet that that's equally likely to set about a collapse.
>As recently as 31 May 2021, China's government has relaxed restrictions even more allowing women up to three children.
[0] https://en.wikipedia.org/wiki/One-child_policy#Abolition
This number is even worse than it appears though, since there are so many more men than women to begin with, thanks to the history of sex-selective abortion in the country. 12 million Chinese women were never born because their parents wanted a son instead of a daughter, and that's an extra 1.3 x 12 = 16 million children that will be missing from the next generation.
China's population is actually predicted to start shrinking in about 5 years.
A little overall population contraction isn't necessarily dire. The concerning thing is a decreasing fraction of the population being working age.
Ultimately, the most dire predictions have China's population halving over the next lifetime, and a sustained, big drop in youth. That's a pretty damning trend.
* Liberalizing birth restrictions can't have any effect on the number of workers until ~20 years later, and in practice much later than that.
* Once the population pyramid has begun to invert, you have fewer people of childbearing age. Reversing the policy cannot replace the children who were not born a few years ago to families who are now beyond the point of seriously considering more children.
* In practice, once having fewer children is socially normalized, it's difficult to have a larger family going forward, and...
* Once you have a severely inverted population pyramid, the cost of supporting elders increases and the economic situation of those of working age deteriorates, which tends to further suppress births.
It takes a long time for these trends to reverse.
Like there are many cases where governments tried to avoid an internal collapse by applying external pressure in form of starting a war.