The solution to people not having enough children is to have more children, you could enlist people from abroad to help with the effort, but you could also try to raise the birthrate using the existing population.

The PRC's total population and working age population will peak in the next five years or so and begin a steady decline from there. 33% of the population will be over 65 by 2050 according to projections.

There was a recent study from Peking University which hypothesized that the population actually peaked in 2018 and is already shrinking. (government numbers are unreliable)

It is estimated to be at 1.4 billion now https://data.worldbank.org/indicator/SP.POP.TOTL?locations=C...

Not just a billion people but millions who are just now entering the workforce