can I drop this year, I can prepare for jee mains 2021. but my marks is less than 75% in up board 2020. I am available for get admission in nit/IIIT collage by JEE.

Hello.
If you are going to take admission in this year in NIT or IIT then your class 12th marks won't matter as per the official notification by MHRD, because as per the decision for this year IIT and NIT have given relaxation to people with no count of class 12th result this year because of the pandemic situation, but it is not cleared yet whether they will be continuing this next year or will they be  following the previous eligibility next year, either it may be through your marksheet which is of pandemic period which will help you to be secure from the 75% case eligibility  or it may be same as before, so I would suggest you to prepare for your examination because the situation would be in favour for the students.
Best of luck.