Many people believe that the Eight Gates can grant immunity to genjutsu, based roughly on two points.
First, after opening the Eight Gates, Chakra becomes extremely violent, meeting the condition of disrupting Chakra flow to break genjutsu.
Second, the Eight Gates continuously damage the user's body, meeting the condition of breaking genjutsu by injuring oneself.
Therefore, they believe ordinary genjutsu has no effect.
But this is all speculation from us Hokage fans or fanfiction authors.
So what would officially happen if the Eight Gates encountered genjutsu?
The answer is that no one knows, because the two have never been seen together.
(Huh?)
My analysis here is based on Guy and Kakashi's explanations during the Chunin Exams, as well as Rock Lee's performance.
Opening the First Gate removed the brain's limitations and unleashed one hundred percent of the body's strength.
Opening the Second Gate removed the limitations of fatigue and forcibly restored stamina.
Rock Lee showed no obvious changes after opening the first two gates, only using the Hidden Lotus.
When he opened the Third Gate, Rock Lee's hair stood on end and his skin turned red, which could be taken as a massive surge in Chakra.
When he opened the Fourth Gate, Rock Lee's body began to suffer injuries, his muscles tearing apart.
Then he kicked Gaara all over the sky.
After opening the Fifth Gate, Rock Lee only made three moves: threw a punch, used his bandages to pull himself back, then delivered another kick. After that, his body was severely damaged, and he collapsed to the ground, nearly unable to move.
So the conclusion is that immunity to ordinary genjutsu may be possible after the Third Gate, but there is no definite answer for the first two gates.
Moreover, even Guy specifically practiced the special technique of judging