There is no rule in zoology that prevents the existence of giant apes
https://es.wikipedia.org/wiki/Gigantopithecus_blacki
The main objection would be the problem of food, since most large apes are vegetarians and Tibet does not abound in this type of food, at least in the amount necessary to sustain a self-sufficient population.
The alternative is a giant carnivore, but no predatory ape is known to exist other than at least omnivorous.
Cold is not a problem as demonstrated by the Arctic Japanese macaques and if an isolated group of chimpanzees had become carnivores due to environmental pressure, it is possible that with enough time they would have increased their size to hunt larger prey.
There is no known rule that prevents the existence of Yeti.
We could even make one with the level of current bioengineering.
But if the Wampa escapes from the lab, Luke Skywalker will need to be called.
View: https://www.youtube.com/watch?v=HA2yWG3tvMw