An Idaho State University Professor has set up a collection called the Relict Hominoid Inquiry to collect scientific papers and analysis on potential extinct or extant great ape species. We recently confirmed the existence of "the hobbit" homo florensiensis, surviving along side modern humans until as recently as 10,000BC or the last great cataclysm of the younger dryas.
I know Bears exist, I've seen evidence of them on hiking trails, but I've never seen one up close. I think the topic of multiple unknown branches of the human and great ape families is
fascinating, and I wouldn't rule out their existence.
Even Jane Goodall is supportive of the idea of extant hominoid species.