There are declining birth rates and then there are collapsing birth rates. Finland and Hungary have dealt with collapsing birth rates. These can certainly be corrected with viable policy.
Anyway, it appears to me that Hungary has corrected their downward projections, so hooray for them:
Finland is still in the muck.
There are some problems still with Hungary's situation that are detailed here, but to atleast some extent, the policies seem to be working:
Hungary’s fertility rates are still extremely low: only about 1.5 children per woman. The government is spending huge amounts of money and will probably never reach replacement-rate with this strategy. However, Hungary is experiencing some fertility gains, probably at least partly as a result of a basket of policy changes including tax preferences, cash grants, loan subsidies, constitutional protections, and costly political signaling. But to the extent these policies are working, they are effective because they are not being used in isolation, but rather together as a whole concert of pro-natal policies and cultural nudges. And they are working because they induce marriage, not simply childbearing, and marriage helps boost long-run fertility, not just birth-timing.
https://ifstudies.org/blog/is-hungary-experiencing-a-policy-induced-baby-boom