Wealthy countries generally do have a decline in birth rates.

There is a lot of fearmomgering and a lot of added lies to it from far right people though.

It is not. More education, more freedom for women to choose a life path, less kids. In some places overwhelming work culture forces this to extreme, where folks focused on career don’t feel they can pursue creating a family at all.

Supremacists often tout “replacement theory” which is fake. It claims there is a conspiracy to actively flip demographics with “immigrants” (read, generally folks who aren’t of their ethic group) to devalue their position in their society. In reality demographic makeup is naturally dynamic and no one is out to get them, people of all ethnicities are just living their lives.

These assholes are all over the world

https://en.wikipedia.org/wiki/List_of_countries_by_total_fertility_rate#Country_ranking_by_most_recent_year

Hong Kong, South Korea, Singapore, China, Ukraine, Thailand, Spain, Japan… Are the countries with the lowest birth rate right now. Not exactly centered around “white supremacist” hot spots.