There is a bit of scholarly debate about the real population of the PRC since COVID revealed some fissures in their population claims.
A couple notes: they had 1 child policy in place since the 1970s and they went below replacement in the early 1990s.
China is hiding a population secret, analyst says | School of Social Sciences
Fertility Decline in China and Its National Military, Structural, and Regime Security: China Population Research | RAND
China's Population Policy at the Crossroads: Social Impacts and Prospects - PMC
China on track for massive population decline