hello aspirant,

Yes, you are eligible for JEE Mains if you have passed from nios also . Students should have passed the 12th class or qualifying examination. Candidates appearing in 12th class or equivalent qualifying exams can also apply.

NIOS is a recognized board if you qualify on demand Mathematics examination from NIOS board yes you're eligible to appear in Jee main . Eligibility - Candidates must passed or appearing class 12 in Physics chemistry and Mathematics with minimum 75 percent marks aggregate from a recognized board.

Further, if you wish to know more detailed eligibility criteria for JEE mains then you can follow thw below mentioned link to know more : https://engineering.careers360.com/articles/jee-main-2022

I hope that this will help