Liberation and Enlightenment

Within Hinayana and Mahayana schools there are different categories and presentations of nirvana.

It’s important to understand that nirvana and enlightenment aren’t the same. Nirvana is the first step. Enlightenment is the second step.

Is it a matter of free will, is it predetermined, does it come from karma or from some other complex explanation?

The Vaisheshika and Nyaya schools share many features in common. Vaisheshika emphasizes the types of entities that exist, while Nyaya emphasizes the types of entities involved in cognizing and proving the existence of those entities.