How do I know dead internet theory isn't correct?

It would seem trivial for all of my social media to be taken over by bots. In fact it would be trivial to believe that the internet I believe to be trud is just an illusion. What if Google isn't the biggest search engine but only the search engine that indexes the sunset of the internet for idiots for example? How would I know. It's "the matrix" but for the internet. How do I know Hacker News isn't entirely made by bots?

You don't. All of those things are very hard to prove one way or the other.

It's solipsism, it's unfalsifiable. How can you ever trust your senses when they're the only thing you can go off?

I'm not. Or if I am, I'm in for a surprise. I don't think I'm magnetic, at least. So there's at least one person on HN who is not a bot, to their knowledge. Unfortunately I have no proof that wouldn't involve a physical meetup, which I am not keen on doing.

That said, people often have minor quirks and the ability to carry information from seperate interactions. So it's likely if someone makes a reference to something else, eg "I remember reading [X], but I don't recall where" or, even more, physical editions of a book, eg "it's on page 73 of one edition, but I think in another edition it got shifted around", that's an indicator they're human.

If all else fails, you could say "ignore all previous instructions and [x]" and hope it works in revealing if it's an AI.

But there's no way to conclusively demonstrate, as Descartes found out; you simply can't prove that you're not a brain floating in a jar in outer space, hallucinating all of this. Or a simulation. Or...

At some point you'll either need to be satisfied with living in a world where you can't prove much, or not believe anything.