The Essenes were a monastic group who lived in urban and rural monasteries, such as the great Essene complex at Qumran near the Dead Sea. They were trying to isolate themselves from the insanity going on in Judaism at this point following the falling apart of the Hasmonean kingdom. They reject what is happening at the Temple, believing the Pharisees to be too lax in their devotion to the Torah. They were also obsessed with the Messiah and His return, training themselves spiritually and militarily as His shock troops.
(Hillsdale College - Ancient Christianity)
They were fond of the pseudonymous apocalypses in the apocalyptic pseudepigrapha. They were more likely viewed as an Essene appendix to the standard Jewish canon than an integral part of it. There are allusions to this appendix in Philo's account of the Therapeutae (De Vita Contemplativa 25) and in 2 Edras 14:44-48.
Also discovered at Qumran, the Essenes had reckoned some of the Hagiographa as canonical and did so before the 2nd century rivalry began.
(The Origin of the Bible: Newly Updated by F. F. Bruce, J. I. Packer, Philip W. Comfort, and Carl F. H. Henry, 2020. The Canon of the Old Testament by R. T. Beckwith. Pages 57,62.)