That wouldn't capture the main driver of population decline for most these countries.

Seems like the primary cause in most cases is /not/ the fact that deaths are outpacing births but, instead, that emigration is outpacing immigration.

Most of these countries are low-income nations in the EU whose workforce is now leaving to flock to higher-income countries.

We're basically seeing a brain drain in EU countries that need that workforce most to drive future growth. One of the unintended consequences of EU membership.