There is a Wikipedia article with this exact title. In fact, I just copied and pasted the title here.

This stuff is broadcasted and discussed on YouTube, in the news sites, etc.

And the general consensus is that population decline is automatically bad for the economy.

People automatically assume that Japan is dying and South Korea is dying. But if you look at the recent data about births, South Korea has 230,000 new births in 2023. In absolute value terms, 230,000 people can sustain a language community. 230,000 people can sustain an economy, but not at the same level as the country once had.

I think the country needs to downsize the economy proportionally. Maybe an earlier generation would have 10 people doing the same job, and the later-born generation would have 5 people doing the same job. As a whole, the economy does get smaller, but it is proportional to what it was before.

Also, there may be more micro-managing from the national government to make sure the sectors of the economy are all proportional to each other. So, Person A will be assigned to Major A in college, and Person B will be assigned to Major B in college. After college, the students will be placed on an internship program to train the newcomers by the old and experienced workers so some workers are allowed to age out of the retirement system and live off of retirement benefits. Otherwise, the old people can't collect retirement benefits, unless the old worker recommends a replacement-person. One person out, one person in.

The overall population will also have to work smarter, not harder, than the older working population. In the past, there might have been 10 factory workers. In the present, there might be 7 engineers, and the engineers would make robots and machines, but because the government oversees everything, the government will analyze the situation and make a judgment whether to allow so-and-so many older factory workers to start collecting retirement benefits. As the older and less educated people start collecting benefits, the younger and more educated workforce will replace the older skilled workforce, with lots of factory jobs being automated.

I am just musing around at this point.

But honestly, I think the global population will eventually decline, and we will just have to adjust to that.

If we have more older folks without children, then the older folks will just pass their stuff to the side branches of the family tree, and that means the children will increase in property and assets, wouldn't they? Wouldn't the per-capita wealth actually increase? A family might have a few old people at the top, a bulging group of middle-aged people and a few children. In some decades, the few old people will die off, and the middle-aged group of people will become old but will live together to support each other financially and socially, and the younger generation will live with their older folks to save on living costs. The younger gen might not have to work as hard as the previous generation because they would already be provided a home and food and stuff, or they might receive some financial assistance in purchasing a home or they might receive some social support in finding a spouse.

I think this idea would take a great deal of planning at the family, local, municipal, provincial and national level, though. The entire country would have to work together.