>very peak of Chinas demographic dividend

No, 2000s-2020s was peak blue collar dividend, think world combined, but low value dividend. When PRC had lots of hands but few brains, i.e. fraction of STEM vs US / west.

2040s-2080s is PRC peak tertiary skilled dividend. They'll have about 2-4x US in just STEM who'll be in workforce for most of our and our children's life times, even while tfr math starts eating away at future cohorts. The TLDR is they've just started cooking, their highend human capita pool will be exploiting greatest high skill demographic dividend in recorded history for high value. Their final form is OCED combined in talent and world combined in bluecollar backstopped by robots/automation (currently on trend to be more than world combined).

Brain drain barely a problem now, this isn't 2000s where there's shit domestic opportunities and PRC lose large % of the few best they produce. They now they mint so much talent, brain drain a rounding error, top talent increasingly stay in PRC. And many of the best that went abroad are returning. Or future trend is many of best that are leaving will recirculate back to PRC eventually. TBH most of those go abroad now are frankly PRC B/C tier talent, i.e. most international students are those too mid to do well on gaokao and even then they turn into A students in west. Like there's still some sectors where west can draw because they can afford to pay magnitudes more (which is matter of FX/geopolitics), but PRC now also in position to attract foreign talent via $$$, so much so that places have to ban nationals from working in PRC strategic sectors. China's expat draw is it's PRC, if you're high end talent and you want lab built in a few months, bottomless access to resources including human capital, dynamism of Asian tier1 cities, that EU+US can't offer. But immigration point really secondary to fact that when PRC produces plurality of high performing global talent, and retains most of them, they don't need to worry about immigration of competent people, just need to hold on people they have, which by and large is happening, i.e. Tsinghua brain drain rate went from 30% to single digits in last few years and returnee rate higher than ever. As in west depend on PRC talent surplus (because western talent pipeline shit vs PRC), trains them, and now that PRC rich with opportunities, many recirculate/reverse braindrain back to PRC anyway when they're high level.

At end of the day _most_ people are economic migrants, they move for $$$ not muh freedom/community. Ultimately US/EU strength is they have money/FX money multiplier, US way more than EU. When that goes away/decline people start making different choices. And again, PRC demographics will be lingering in background... but just means cheaper housing/less crowded cities, i.e. less drag on PRC living. It terms of active demographic dividend, most of us will be dead before PRC declines, imo not really worthwhile extrapolating on that timescale.