Nirvana cannot be a process because this would make Nirvana 'conditioned'.
Nirvana is a state (dhamma; ṭhānaṃ) or a sense object/base (ayatana; Udana 8.1).
There is, bhikkhus, that base (ayatana) where there is no earth, no water, no fire, no air; no base consisting of the infinity of space, no base
consisting of the infinity of consciousness, no base consisting of
nothingness, no base consisting of
neither-perception-nor-non-perception; neither this world nor another
world nor both; neither sun nor moon. Here, bhikkhus, I say there is
no coming, no going, no staying, no deceasing, no uprising. Not fixed,
not movable, it has no support. Just this is the end of suffering. Ud
'This Dhamma that I have attained is deep, hard to see, hard to realize, peaceful, refined, beyond the scope of conjecture, subtle,
to-be-experienced by the wise. But this generation delights in
attachment, is excited by attachment, enjoys attachment. For a
generation delighting in attachment, excited by attachment, enjoying
attachment, this/that conditionality & dependent co-arising are hard
to see. This state (ṭhānaṃ), too, is hard to see: the calming of all
fabrications, the relinquishment of all acquisitions, the ending of
craving; dispassion; cessation; Nibbana. MN 26
standing; the act of standing, being fixed or stationary; continuance.
a place; a locality; a spot; a site; a location; a suitable place; a
worthy object. region, sphere; metaphysical or spiritual state.
situation; station; office; position. position; state. occasion; case,
occurrence; matter. quality; attribute, characteristic. ground, basis;
reason, cause. stance; standpoint; condition.