I'd also note that plummeting birthrates are also happening in countries that are known for great social welfare, lots of government support for new mothers, and a more egalitarian society overall, like Finland. A lot of people simply don't want kids. Kids take a huge amount of time and investment for about 2 decades of one's life, and that can have a large, significant negative impact on quality of life, especially…
It is also true that societies are brutally darwinian. The ones that prevail are the ones that can produce the most offspring, and bring it to economic maturity.
This is the story behind the enormous success of China and India, per capita they are relatively poor but punch well above that weight since they have enormous populations. If they can sustain that population dynamic (which seems problematic actually) then it doesn't matter that they are per-capita poor. They are still nuclear superpowers with lunar missions. It doesn't matter if they are illiberal, there are more of them.
It feels like for all its faults, the global West has values worth preserving for the future, and that involves, well, going through with it and making babies.
But then I suppose, the burden of childcare should be better socialized. It used to rely more on grandparents, who would live nearby and be a good 10-20 years younger than nowadays.
But then again, you're saying, where that is in place people still don't want to have children. So maybe that doesn't work either.