Nonhumans can & do attain nibbāna.
https://dhammawheel.com/viewtopic.php?f=13&t=30969
Digha Nikaya 21
Sakkapanha Sutta
The Questions of Sakka
Sakka, the deva-king, asks the Buddha about the sources of conflict, and about the path of practice that can bring it to an end. This discourse ends with a humorous account about Sakka’s frustration in trying to learn the Dhamma from other contemplatives. It’s hard to find a teacher when you’re a king.
…
Then Sakka, the deva-king, touched the earth with his hand and said three times, “Homage to the Worthy One, the Blessed One, the Rightly Self-awakened One! Homage to the Worthy One, the Blessed One, the Rightly Self-awakened One! Homage to the Worthy One, the Blessed One, the Rightly Self-awakened One!”
While this explanation was being given, there arose to Sakka the dustless, stainless Dhamma eye — “Whatever is subject to origination is all subject to cessation” — as it also did to [his following of] 80,000 other devas.
Such were the questions that the Blessed One answered at Sakka’s bidding. And so this discourse is called “Sakka’s Questions.”
https://www.accesstoinsight.org/tipitaka/dn/dn.21.2x.than.html
then is it possible?
Nonhumans can & do attain nibbāna ???