A certain Brahman (lay priest, as he uses this term) here told:
Nibbana is simply what is experienced by the mind which is free from defilements and fetters. It is not an Ultimate Reality or Ultimate Truth.
So according this, Nibbana isn't real but something, a maybe 'unconditioned Mind' experianses, and mind is obiviously assumed to be real.
What did the Buddha told in regard of Nibbana and Mind?
"Nibbānaṃ anicca. Cittānaṃ saraṇaṃ hotu."?
[Note that this isn't given for stacks, exchange, other worldbinding trades or to entertain the mind, but for an escape to lasting freedom from debt]