If you have Mathematics in your 10+2 score then without any doubt you are eligible for the admission in NIT's. See in the best 5 score, the Mathematics score may get out of the aggregate score, but this doesn't mean that it turned to your additional/optional elective subject.

For more information regarding the JEE MAINS 2022 consider the link provided below:

https://engineering.careers360.com/articles/jee-main-2022

I hope this helps. Wish you a great day!