A world where there are fewer humans who can ever understand math is the world with less mathematics.
Mathematics represents the rational skeleton that upholds and stabilizes our vague, formless but far more common belief-based thinking.
Without it, losing it from neglect, we would collapse back into a pre-rational state of fantastical, wishful thinking.
Pretty much exemplified by large parts of US society already, but there is no bottom otherwise keeping society from collapse.
> What would such a world look like?
Major religions, minor religions, cults will have a field day. Or more like a field century or a millennium or twenty, who knows.
Up to a few years ago, I would see or read some science fiction that was medieval times with spaceships (ala Dune) and I would roll my eyes and think “ffs, can’t people move on and invent something more original?”. Now I seriously believe that’s one of the most benign futures waiting for our species[^1]. Not that there aren’t lots of lights in this tunnel, it’s just that its shadows are very black.