This is true, but it’s not like South Korea will just be producing slightly less consumer goods. Their population will soon be majority senior citizens. These seniors need people to provide and care for them. I’ve read estimates that even if every working South Korean quit their job and became a nurse, there still wouldn’t be enough nurses to care for the elderly population. Of course, every single worker in a country being a nurse would be a terrible idea, but it just goes to show how lopsided their demographics are.
The biggest issue here is that, ironically, South Korea’s older population is staunchly against any and all forms of immigration. South Korea isn’t the only country filled with old people, but they’re one of the only ones that refuse to import young people from other countries in order to balance things out.
These studies warning of collapsing economies are a way to try and persuade South Korea’s old people to allow immigration before their country collapses.