100 000 000?

That is a huge number - I accept there are likely very many Americans with assorted, ill-defined "world-ending" notions; "survivalist" bunker mentalities, Book of Revelations believers and the like; but around a third of the population seems too many.

Where did you find that estimate?

I wonder what apocalyptic notions they hold, and why. I expect there will be many, between them.

For example,the planet's destruction by some imagined astronomical event, most of Earth's life exterminated by some other astronomical event; world-wide pandemics far more dangerous than any we have see so far (including Bubonic Plague and Covid), societies across the world collapsing as resources run out, an intractable world-war rather like Orwell's setting for his 1984....

..... or are a lot of 'em simply Americans afraid of losing the cosy all-American way of life?