Yes, Brahman is formless.
I.5 - You do not belong to the Brahmana or any other caste or to any ashrama. You
are not perceived by the senses. Unattached, formless and witness of all are you. Be
I.17 - You are unconditioned, immutable, formless, of cool disposition, of
unfathomable intelligence and unperturbed. Desire Consciousness alone.
I.18 - Know that which has form to be unreal and the formless to be permanent.
Through this spiritual instruction you will escape the possibility of rebirth
VII.3 - In me, the boundless ocean, is the imagination of the universe. I am quite tranquil and formless. In this alone do I abide.
XVIII.57 - The sense of duty, indeed, is the world of relativity. It is transcended by the
wise who realizes himself as all-pervasive, formless, immutable, and untainted.