I don't really see how this is different from "LLMs can't multiply 20 digit numbers"--which btw, most humans can't either. I tried it once (using pen and paper) and consistently made errors somewhere.
People made missiles and precise engineering like jet aircraft before we had computers, humans can do all of those things reliably just by spending more time thinking about it, inventing better strategies and using more paper.
Our brains weren't made to do such computations, but a general intelligence can solve the problem anyway by using what it has in a smart way.
I'd wager that 95% of humans wouldn't be able to do 10x10 multiplication without errors, even if we paid them $100 to get it right. There's a reason we had to invent lots of machines to help us.
It would be an interesting social studies paper to try and recreate some "LLMs can't think" papers with humans.
With enough effort and time we can arrive at a perfect solution to those problems without a computer.
This is not a hypothetical, it was like that for at least hundreds of years.
But then you're not measuring the ability to perform the calculations, but the ability to invent the methods that make the calculation possible.