The difference between Arupaloka and Nibbana

Q1) What is the difference between Arupaloka and Nibbana except Nibbana has no incarnation, no dukkha and has Buddhism teaching ?

Arupaloka beings still attach to their "atta" (self conception).

What is the difference between Arupaloka and Nibbana except Nibbana has no incarnation, no dukkha and has Buddhism teaching ?

The arupa ayatanas are the subtle enclaves of the coarse human consciousness. The word consciousness here means the continuum of experience derived from the arising of sensate phenomenon, which is more accurately described using the five aggregate model: with the arising of form, feeling/perception come into play from which two reactions arise: aversion and attraction. In this world/body relationship consciousness becomes a self-replicating repository, and it is in its very ability to self-replicate that one finds a continuum called Sue, Bob or John. Those entities then haul around the regrets of their history - which is akin to hauling around a slab of concrete - and make feeble attempts to offset these regrates by projecting favourable images of a better future. In essence, it is a neurotic consciousness where one creates a stressful here and now. That is the delusion, and that is what Dogen calls The Ten Thousand Things.

This is a very noisy situation - so noisy that one cannot discern or even conceive of another way. Practice aims to reduce this type of noisy consciousness so that illuminating knowledge of another way can be discerned. Once one has reduced a substantial degree of this type of consciousness, you enter into the arupa ayatanas. A comparison between the arupa ayatanas and nirvana only serves a mind intent on food for thought. It gives something for the mind to lick - like an ice cream. It is better to not alight on anything with regard to comparisons.

Q2) Why brahmas unable to hear the teachings of the Buddha at Arupaloka?

They don't have ears... but to bring an answer closer to earth in terms of meditative qualities: it is only the last two arupa ayatanas where one cannot discern a state, a non-state, or neither a state nor a non-state simply because the consciousness there is extremely tenuous. In other words, a teaching cannot be accessed. It is only in retrospect that can one come to understand the last two arupa ayatanas; when one has emerged from those states, then it is possible, by means of reflection, to know those states. But when you are in those states, you cannot be taught anything. Regardless, the mind is radically changed by such subtle types of consciousness. It becomes a wafer several microns thick, primed to snap at the mercy of the lakshanas.

The difference between the formless realms and extinguishment is the degree of emptiness. In MN121, the Buddha advises Venerable Ānanda on the progressive stages of the meditation on emptiness. Here is the transition leaving the realm of form:

MN121:6.1: Furthermore, a mendicant—ignoring the perception of wilderness and the perception of earth—focuses on the oneness dependent on the perception of the dimension of infinite space.

In the above, the perception of wilderness is unsatisfactory in its impermanence, so it is natural to proceed onward to the formless. Indeed, the meditation on emptiness proceeds deeper and passes through the formless, leaving it here:

MN121:10.1: Furthermore, a mendicant—ignoring the perception of the dimension of nothingness and the perception of the dimension of neither perception nor non-perception—focuses on the oneness dependent on the signless immersion of the heart.

In each transition noted during meditation, the preceding stage is perceived as unsatisfactory and impermanent. Relinquishing each attachment opens up greater freedom. Indeed, the transition out of the formless is the eighth and final liberation.

DN34:2.1.206: Going totally beyond the dimension of neither perception nor non-perception, they enter and remain in the cessation of perception and feeling.
DN34:2.1.207: This is the eighth liberation.

Note that the conceit "I am" still permeates the formless. The observer still sees. When the observer sees, there is "this and that". With "this and that" in mind, perception and feeling still bubble and perturb. That perturbation is disturbing and unsatisfactory because it is also impermanent--"that" appeared and "that" will disappear. If "that" is impermanent, then "this" might also be--that attachment to "this" causes anxiety. So one might attempt to perfect the formless, but that is pointless, an unsatisfactory dead end. Those who are stuck in the formless, are unwilling to accept "this" as impermanent. They cling to the notion that somehow perfecting the formless will lead to a subtle perpetuation of "this". But just as "that" appeared and disappeared, so too must "this".

Only in letting go of "this", the conceit "I am", does suffering cease:

DN34:1.4.27: Renunciation is the escape from sensual pleasures. The formless is the escape from form. Cessation is the escape from whatever is created, conditioned, and dependently originated.