Dear aspirant

Naturally Class 12 certificate is very necessary for sitting in JEE ADVANCED  couselling.

Mandatory cut off  score is usually 75% i.e. one has to score a minimum percentage of 75% in class 12 board exams along with qualifying jee advanced to get a seat for top IITs.

But this year the scenario has changed. Due to corona virus pandemic +2 exams of many state boards has been  either delayed or postponed. That's why many students can face serious problem. A month ago union HRD minister Dr .Ramesh Pokhriyal tweeted that due to the problem mentioned before that JAB is considering to relax the eligibility criteria for this year. So cut off percentage of 12th will be omitted most probably, however 12th marksheet is still necessary.

check here for further details

https://engineering.careers360.com/articles/jee-advanced-eligibility-criteria

Best of luck.