I think it is pretty well established in Buddhist circles that nirvana is unconstructed (asamskrita). It falls on the side of the unconditioned whereas, by contrast, the world of samsara (birth-death cycle) falls on the conditioned side which is to say that all things are impermanent or anitya.
Odd to me, in Nagarjuna’s Mulamadhyamakakrika (hereafter MMK) we find this karika of his.
“Samsara (i.e., the empirical life-death cycle) is nothing essentially different from nirvana. Nirvana is nothing essentially different from samsara” (MMK XXV, 19, trans. K.K. Inada).
Put another way, Nagarjuna is saying conditionality is essentially nothing different from unconditionality. Unconditionality is nothing essentially different from conditionality.
Maybe at a strictly linguistic level we can get by with this insofar as both terms are merely signs that point to abstract concepts. But for one, like the Buddha, who has realized actual nirvana and for one who is still entangled in samsara, there is considerable difference. The monk who is freed from desire and attachment; who has attained the immortal, the tranquil and deathless state of Nibbana (cp. Sutta-Nipâta 204) there is a huge difference from the monk who has not.
Adding this up, it is not true that there is nothing essentially different from the deathless state of nirvana and the birth-death cycle of samsara. The difference is a spiritual difference as far as actual realization is concerned. I hasten to add this, but some of what Nagarjuna said, the Buddha never said. Incidentally, this is why I stress reading the Nikayas/Agamas first.