Yetis,( or bigfoot or Sasquach) could be real alright. This story has emerged in several different places all around the world. In Africa this could just have been explorers seeing gorillas, as some of the drawings are very similar to gorillas.
But in other places there is not an explanation like that. Some “cyptozoologists” think that it could be some remaining Neanderthals living in the wild.
However, in my opinion, the chances of us not officially discovering one, with all the people in the world now, are pretty slim. So I’d unfortunately say that they don’t exist. But maybe you should become a scientist and try find out!