And if they’re not as xenophobic as some other countries I could mention, they could easily solve the population issue through immigration.

Every Chinese book I've read screams at me nationalism and xenophobia, be it modern fantasy, 50 years old detective series or comedy.

And immigration to China is - currently - heavily restricted. Like damn heavily. And you will not become a permanent resident, and there is literally 0 chance of becoming a citizen, unless you're of Han Chinese descent, preferably first generation, preferably looking Chinese, and you can't have dual nationality (from last census in 2020 about 17.000 people ever got a citizenship, which is what. 0.0012% of population? And the permanent residency in 2017 was about 10k total).

My country, Poland (about 38m people), grants more than that every year.