Is “Judeo-Christian civilization” a historical reality… or a modern political invention?

I’ve been reading arguments claiming that the idea of a shared “Judeo-Christian civilization” is much more recent than most people think.

For the past forty years or so, “Judeo-Christian civilization” has been presented as the cultural foundation of Europe and North America.

The thesis is that Judaism and Christianity spent centuries defining themselves against each other, often in conflict, and that the expression “Judeo-Christian” only became widespread in the 2nd half of 20th century for political and reasons.

If that’s true, then why is the term now so often presented as if it described an ancient, self-evident civilization?

I’m curious how historians and people familiar with the subject see it. Is “Judeo-Christian civilization” a useful historical concept, or is it mostly a modern narrative?