Is Nibbana a different reality, or just a different state of mind?

Moksha in Adwaita is gaining union with Brahman, who is posited as the intelligent creator of the world. This is incompatible with the Buddha’s Teaching, which advises one to put aside the question of creation of the cosmos. No motive is assigned to Brahman, though - apparently it’s all just sport and play.

From the Brahma Sutras :

Adwaita rejected the Buddha’s Dhamma as a bunch of unintelligible nonsense and considered the Buddha as a malevolent person.

From the Vedanta Sutras :