South Korea is one of the countries that suffers from the problem of decreasing the number of births, and therefore the continuation of policies such as one child and others will make the proportion of the elderly exceed 20% in the next few years
South Korea never had a one-child policy on the same level as China, what they had was a campaign on having no more than two but which was not enforced at any level, it was promoted a lot but still, some had more than two children, it's nothing like China and the fall is far more linear, based more on economic and social development rather than penalties and government policies. From the link you've quoted:
In the 1960s, the South Korean government launched programmes to curb fertility, encouraging the use of contraceptives and promoting a two-child norm.
It was just encouraging and promoting, and even without it would simply have delayed the inevitable, every single country is moving towards that except for parts of Africa, but that will change also in less than a decade and probably the shock will be even worse.
This thing is unavoidable and I don't think any crypto hub or whatever will change this if it would have worked California would have managed to avoid a halving in fertility rate since the '90 with all those tech hubs, but it ain't working at all.