The number of things that ACTUALLY exist is vanishingly small compared to the things people CLAIM to exist, but I do believe there are at least SOME cases that genuinely cannot be explained, or at least, not based on our current understanding of the world. Things like ghosts, demons, angels, the human heart and soul... While I certainly understand the desire to do so, I'm not content to write such things off as being no more than delusions or the products of chemical reactions. The world deserves at least that much.
As far as most CRYPTIDS go... I personally err on the side of "eh, probably not, but who knows?" For one thing, the absence of evidence isn't evidence of absence. For another... Well, the idea that creatures like Bigfoot or the Mongolian Death Worm have existed in near-complete secrecy for hundreds or even thousands of years isn't as outlandish as it might seem at first.
Think about it: it wasn't until 2019, after more than a CENTURY of searching, that a living Fernandina tortoise was found, long after the species was believed to have gone extinct. Fernandina Island is less than a tenth of the size of Yellowstone National Park. Not only is it completely barren and open on much of its landmass, it's damn near as flat as it gets. And it took 113 years to discover otherwise.
So, again. It's not at all a leap to think something like a "Bigfoot" or "Mongolian Death Worm" could genuinely exist. I'm not convinced, mind you, but I'm not willing to dismiss the notion outright, either.
Lastly... Extraterrestrial life clearly exists. Just look at "people" like Mark Zuckerberg!
Jokes aside, for all the obvious hoaxes and crazy hobos you hear about, there ARE some genuinely perplexing cases, too. I'm not going to get too far into that topic here, but suffice it to say, I'm fairly convinced first contact has already occurred. Probably a long, long time ago, even. What that actually means, however, is far less clear to me.
