I gave 12 board with cbse in 2019 and jee advance 2019 and 2020 but not qualified ,can I give 12 board again in 2021 with cbse to gain one more chance in jee advance.

Dear student,

As you have given JEE advanced two times, then as per the maximum number of attempts your all attempts are over. You passed your class 12th in 2019, then your first attempt for jee advances was over in 2019. And as you give second attempt in your first drop, that is in 2020, therefore your second attempt is over. Now you are left with no more attempts in JEE advanced but still you have one more attempt left in JEE Mains.

Now if you think that you can give once again the board exams is 2021 then you are absolutely wrong it is not possible because there is only one criteria that if you are not satisfied with your board results then you can give improvement exams in next successive year or compartment tests.

But with two years gap you cannot give board exams once again to gain a chance or attempts in JEE advanced.  So it is not possible, now as you have not qualified in JEE advanced, then still, as you have given JEE mains, then you can get colleges on the basis of your JEE mains rank and as your one attempt is left in jee mains then you can give JEE mains 2021.

Also check out our jee mains college predictor tool to get an appropriate idea of colleges that you can get on basis of your jee mains rank :-
https://engineering.careers360.com/jee-main-college-predictor?icn=QnA&ici=qna_answer