I had PCMB in 12th(passed out in 2020). But as my Maths number was lowest among them, so according to WBCHSE's best 5 Marks criteria my Maths automatically became Optional Elective Subject. That means as per Eligibility criteria I can take admission in NIT ?
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!