Hello Aspirant,
Only for this year in the wake of COVID-19 pandemic government and the competent authorities responsible for JEE provided the relaxation of class 12th marks to appear in JEE-Advance. Now if you want to appear for JEE-Advance 2020 you only have to clear the cut-off of your category in JEE-Main and should have passed class 12th, there is no any restriction of marks of class 12th.
Note that this relaxation is only for this year, from the next year JEE-Advanced and JEE-Mains will be held as usual.
For admission to IITs you should compulsorily appear in JEE-Advanced. It is known that for this year JEE-Advance is scheduled on September 27th 2020.
I hope this information helps you.
Good Luck!!
Regular exam updates, QnA, Predictors, College Applications & E-books now on your Mobile