The problem isn’t the absolute number of humans. The real issue is the dependency ratio.

Dependency rationalizes itself with acceleration of death rates.

I don’t know what “rationalizes” means, but more deaths don’t necessarily lower the dependency ratio.

For example, a war would kill lots of young healthy soldiers, leaving even fewer people in to care for the old, young, and infirm.

I’m guessing Ukrainian and Russian dependency ratios are getting worse and worse.

China deliberately lowered its fertility to a below replacement level. A few decades later, they decided they wanted to raise it back up higher.

They couldn't. They're not exactly wishy-washy, they happen to be one of the most authoritarian regimes on this planet, even if they understand the benefits of a velvet glove. If they couldn't raise it, why would you think anyone else can?

And we're already at sub-replacement. The same people who make the next generation of people (as small as it is), are the ones who also raise that generation and instill their values in them. What does having one child teach that child about their parents' values? It teaches them that, at most, they should have just one. Or maybe even that they should have none at all. Not only is this a self-reinforcing problem, it accelerates. You don't have a few decades to solve this.

Nor will "evolution" fix it as the other guy said. While some still have large families, it's not just the parents' own values that are instilled, but that of our society collectively. The many who have few or no children have far greater influence on the children of those families, than those families have on everyone else.

Population is counter-intuitive, and none of you understand it.

You're making all these assumptions about how the population grows and shrinks on a tiny subset of human history. People are not going to disappear as a species from social trends like having fewer children. Society will change to accommodate the new status quo and reach an equilibrium, like it has for the entire history of the species. Whatever wipes out humanity, it won't be that.

It’s worth noting that the they only put population control measures in place because their prior policy of encouraging massive population growth backfired horribly due to the strain it wrought on society’s carrying capacity.