Not to take this thread off topic, but at least let me offer a glimpse of a comparison of the changes relative to China's, to stay relevant to the topic:
This is from the report you linked, where the real finding is the timing of births, and not to any demographic instability:
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A fertility rate of 1.6 is not exactly a "crikey" moment, considering its long term stability, and in view of the rising population overall, with data up to 2020 below. The latest dip is short term, and coincides with economic cycles and Covid. The recent changes will be short lived and are not going to affect the long term demographics significantly.
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The magic ingredient is immigration, which is a benefit China has denied itself due to its nature of being a closed xenophobic authoritarian society. Hence the demographic troubles it is facing over the remainder of this century, at least.