Hello Aspirant,
Yes, you will be definitely allowed to sit in JOSAA counselling as the cutoff for jee mains is released for those who are qualified to sit in Jee advanced exam. This doesn't mean that you can not participate in the counseling as a seat is given according to the rank and availability, a person with high percentile can make it to the NITs and other GFTIs even without qualifying mains.
Good luck!
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