As an immigrant, grandson of an immigrant on one side and great-great-grandson of an immigrant on the other side, I agree: it's a super complex issue all around, eh? Interesting to hear Finland is having problems with the birth rate too. Of course Japan famously has been having this problem for yers, but I wonder if the rest of the developed world has caught up, so to speak. Most years it is still a slight negative here, with more deaths than births—and virtually no immigration, so society is shrinking, but I think it has also stopped falling as dramatically as many feared, even with the massive inflation of the past few years.
It has never been that high, but it has been severely cut in the last 15 years. The social media years. At some point, Japan will balance as the old die and things will be okay there. Just have to ride it out a few decades.
In Japan they aren't sensitive to those issues because they have next to no immigrants and negative demographic trends aren't that noticeable. Besides, Japan has made huge strides in robotics and automation, which in the long run, reduces the need for that many people. I've seen some Japanese claiming that shrinking population isn't such big deal, because Japan with under 100 million people has functioned well in the past, so it can function well in the future.