Hari om, you are asking a question as to : “ Is 84 %a good score in the CBSE class 12, 2019?”. Hari om. Hari om.
ANSWER :
Yes, if 84 %is not a good score in CBSE 12th Class, I would call it a very good score.
Your eligibility even for IIT, NIT, IIIT admission is only 75 % in the aggregate.
So, you are even eligible for IIT JEE Mains. Marks are not that important compared to your knowledge of concepts in PCMB subjects.
Keep in touch with the subjects till you get admission in some college. All the best. Hari om.