Today it takes so many fewer workers to produce a "widget" than 20 years ago. (China Labour Productivity Growth data is updated yearly, from Dec 1953 to Dec 2022, averaging at 7.40 %)
https://www.ceicdata.com/en/indicator/china/labour-productivity-growth
Advances in AI and automation are going to accelerate this trend in the future, so concerns about the worker to retiree ratio are misplaced. As far as excess men, yeah the enforced one child policy really messed up that with some social consequences. However, crime rates in China are low so clearly all these excess men aren't going to topple society.
The bottom line is that the proven dangers from global warming and species extinction are a far greater threat to all of us than any of the concerns commonly brought up when declining birth rate are discussed. Furthermore you need to ask yourself why population numbers are never challenged by the global elites. We are both consumers and labor units to the owners of capital. The more of us the lower labor costs and greater the consumption of all the crap they sell us. We can either begin to institute VOLUNTARY birth control, starting with ensuring infant survival (if a woman thinks her kids have a good chance of reaching adulthood she will have fewer children). We then need to educate every woman on the planet to a highschool graduate level (Educated women have fewer children.) Beyond that we can pay women a stipend every year they do not give birth and incentivize men with a payment for vasectomies.