Nations of varying demographics and economic ranks will not be able to avoid the consequences if these trends are allowed to continue. Lower-income countries must offer better access to contraceptives and female education, and wealthier nations must prioritize policies that support a robust social security system and open immigration to maintain population size and economic growth. Otherwise, the world will be in deep trouble.
Lower fertility rates don't pose an existential threat to the planet because a shrinking population could alleviate strain on global resources and reduce carbon emissions. These studies tend to over sensationalize the socio-economic consequences of slow fertility rates, which can lead to more restrictions on women's rights to contraception and to pursue education and work over having a family. There's no fertility crisis just yet.