I'll try to slightly dive into Advaita philosophy here. Both the Upanishads and the Yoga Vasistha affirm that the distinction between the seer and the Self is an illusion created by the mind. When this illusion is dispelled, the oneness of the Self is realized. The intellect, which seems to function as a separate tool, is ultimately part of the same illusion. True knowledge is realizing that there is no separation—everything is the Self.

Quoting one from Katha Upanishad 1.3.10:

"Indriyebhyaḥ parā hy artha, arthebhyas ca param manah, manasas tu parā buddhir buddher ātmā mahān parah"

Translation: "Beyond the senses are the objects, beyond the objects is the mind, beyond the mind is the intellect, beyond the intellect is the Self."

This quote emphasizes that the intellect is still a part of the illusion. Beyond even the intellect lies the Self, which is one and undivided.