Why is Nibbanna unconditioned if it's dependent on mind & brain

In Buddhism, all conditioned constructs can be eliminated because they are directly observed as - the same epistemological commitment as the scientific method - not substantial and not permanent.

To achieve nibbana, wrong view is eliminated. A well defined, permanent Self (not an operationally defined one for practical purposes) is the incorrect view that is eliminated.

Rovelli's relational quantum mechanics does just this, and EPR vanishes.

Now were this world somehow one of permanent entities, Dhamma would be wrong, the Buddha would be wrong, and either nihilism, or some eternalist religion would offer the right path to the abandonment of stress (notice the instant contradictions). But this world is empty of permanent entities, so elimination of all impermanent properties is possible.

Greed, hatred and delusion can be eliminated. For example, if you see a beautiful girl then sensual desire or greed might arise but if you see a very ugly women then sensual desire will not arise. Nibanna is not dependent on anything. If you know that the beautiful girl will one day age and become ugly you won’t feel any sensual desire or greed. So greed, hatred and delusion comes from ignorance. Nibbana is the cessation of ignorance

Knowing & experiencing Nibbana is dependent upon "the brain" or having a mind. The suttas (example Udana 8.1) say Nibbana is a sense object or 'ayatana'.

However, Nibbana itself, which is an element of nature, similar to how oxygen or nitrogen are elements of nature, is not dependent upon the brain; just as the elements of oxygen & nitrogen in the universe is not dependent on brains.

Many 'Buddhists' hold creationist views of godly Brahmanism; believing things exist only when they can be known by a mind.

But the Buddha said in AN 3.136 and SN 12.20 that realities can exist despite being unknown to a human mind.

Often it is said that nibbana is unconditioned

True, Nibbana is unconditioned

but nibbana is definitely dependent on other conditions

False. This statement cannot be backed-up by any reference from Pali canon.

Also, according to modern psychology........

You cannot explain Dhamma with modern Sciences.

WHY??

There is a true nature in this world. That is the nature of causes and effects. An effect is made by many causes and that effect will cause many other effects in several ways. (This is a very complex, hard to understand, hard to see, and very deep truth which has been taught in the "Book of Causal Relationships or Patthana Pakarana" in Pali canon. There have been mentioned 24 modes of conditionality). Only a lord Buddha can see this ultimate truth with his own wisdom without the guidance of a teacher. No other can.

Scientific method is the foundation for all modern sciences. In scientific method you carefully observe something or a pattern in the world.

Observation:

Once learned, never able to unlearn.

Then a hypothesis is developed upon that observation.

Hypothesis:

nothing can be 'eliminated' (greed, hatred and delusion,...)

Then a prediction is developed and carried out an experiment to prove the hypothesis. At the end a conclusion has been made whether the hypothesis can be rejected or cannot be rejected. There lies the limitation of scientific method. An experiment can only support a hypothesis but cannot prove the hypothesis. So, a hypothesis can be true only under the conditions which the experiments carried out to support it. This is the reason one hypothesis is criticized and proved false by another over the time.

Scientists may explain a natural phenomenon with theories well supported by extensive amount of researches. And yes, that would have been true for a while until they find another behavior within that phenomenon which cannot be explained with the same theory. For example some phenomenon cannot be explained with Newtonian Physics but they can be well explained with Quantum Physics.

Dhamma cannot be criticized or argued. It is true for all the time.