At current fertility rates, Europe's population is going to halve in 3 generations, and who remains is going to be quite old on average. I don't know your age, but if you're young enough this will happen within your lifetime. It's not a distant and abstract problem.

I am not accounting for immigration of course, but from the wider point of view, immigration is musical chairs. Sri Lanka is well below replacement and still falling fast. Who is going to immigrate there? Ditto for most other countries.