Was he immune or resistant to Genjutsu?
Specifically Uchiha Genjutsu?
He never fought an itachi in his life, so genjustus were good enough to kill him yet
Maybe his Sage mode made him immune. Lets not forget Genjutsu causes a disruption in the victim Chakra so if Sage mode is enabled he is always connected with nature and balancing his chakra.
We never saw Sage mode naruto being under Genjutsu. Just base Naruto..
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that sounds directly similar to sakura.
He is not resistant to genjutsu, no one is unless they have a foreign chakra in their system (like Jinchuuriki for example). Genjutsu is induced by inserting once chakra into the opponent, breaking the equilibrium between their physical and spiritual energy thus putting them into a genjutsu. You break out of the genjutsu by spiking your chakra (sudden pain, the Kai technique which produces a spike in the chakra circulation thus restoring the balance etc).
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Sagemode senses danger and his escape art allows him to avoid frontal attacks but no counter can be made when already placed in a genjustu at a high level
Nope.