>nothing that any country is trying is working.

Because most countries aren't actually trying anything nor can the government do much in that regard when the issues are cultural and emotional.

The low-birthrate couples who can't/don't want kids aren't suddenly gonna want them if you give them 3 months of paid maternity leave and a monthly stipend or other such welfare perks.

And those who do have kids because of government welfare perks, were having kids anyway, they're now incentivized to have even more.

3 months of leave or a small welfare payment are not sufficiently compelling alternatives to a career. Pay them at the level of a career and see if that changes the numbers - I feel like at least some people would be interested in that. (Say, median national income? Spitballing here)

The countries that do try seem to fall short of actually replacing even a few years of serious career work and offer no way to go back to that career after taking care of children for a while, so you just need to do that.