Cryptozoology is a pseudoscience and subculture that searches for and studies unknown, legendary, or extinct animals whose present existence is disputed or unsubstantiated, particularly those popular in folklore, such as Bigfoot, the Loch Ness Monster, Yeti, the chupacabra, the Jersey Devil, or the Mokele-mbembe. Cryptozoologists refer to these entities as cryptids, a term coined by the subculture. Because it does not follow the scientific method, cryptozoology is considered a pseudoscience by mainstream science: it is neither a branch of zoology nor of folklore studies.
All the animals you've mentioned here were well known for decades (even centuries) before the (pseudo)science of Cryptozoology was established in the 1950s.
It is absolutely pseudoscience. The only subjects of study are creatures that have no concrete evidence of existence. In the 75 years since the establishment of the 'discipline', no new species have been documented by cryptozoologists. Meanwhile, actual biologists discover (and more importantly document) hundreds of new animal species every year.
Even if some famous cryptid were to be proven to exist, it would immediately be no longer a cryptid. They're just animals, and would be studied by zoologists just like Komodo dragons are.
Perhaps pseudoscience is too strong a word. It only becomes pseudoscience for me when it involves deception (such as portraying nonscientific narrative approaches as being motivated by the scientific method), but people have different bars for it
I feel like "esoteric" field of science or the like makes a lot more sense.
While it's a small field that few serious scientists are devoted to, they used and use scientific methods to find a lot of animals previously thought to be myths.
Maybe it doesn't involve fabricating evidence but at least it is very much based on trusting sources that are obviously nonsense.
There are mythical phenomena that have a real explanation but those have been investigated because they are described in many independent documents.