While it's true that Japan and Italy are the only two major developed countries suffering actual decline, basically all of the big wealthy countries are experiencing fertility below replacement.
https://data.worldbank.org/indicator/SP.DYN.TFRT.IN?location...
Fertility, total births per woman 2021
Australia 1.7
EU 1.5
UK 1.6
Japan 1.3
Korea 0.8
US 1.7
Replacement fertility is estimated at 2.1. Countries with below replacement fertility are growing based on immigration.