I am extremely sorry to tell you dear but you are not eligible for JEE mains 2021 examination.
This is because,
One can give JEE Mains entrance examination for a maximum of 3 consecutive years starting from the year of passing 12th board examination.
So, if you have passed your 12th in 2018 you are eligible for only JEE mains 2018, 2019 and 2020.
You are not eligible for JEE mains 2021 as
Eligibility criteria says that to be eligible for JEE mains 2021 for BE or Btech you just must be either appearing for 12th board exam in 2021 or should have passed it in 2020 or 2019 with Physics, mathematics and anyone of Chemistry or Biology or Biotechnology or Technical Vocational Subject.
i hope you are well
sorry to say but you are eligible to appear for JEE mains 2021 as the basic eligibility criteria says candidate must have passed their 10+2 from recognized board in 2019,2020 or appearing in 2021 are also eligible and candidate can take up exam maximum for 3 years consecutively and can sit for both january and april session.
hope this helps!
No you are not eligible for JEE Mains 2021 as you have passed your class 12 in 2018. A student can appear for JEE Mains for three consecutive years, the first year being the year you passed your class 12 that is 2018. So you could have appeared for JEE Mains in 2018, 2019 and 2022.
Also, a student can appear fire JEE Advanced for two consecutive years. So you are not eligible for both JEE mains and JEE Advanced
You can find detailed eligibility criteria for JEE mains here https://www.google.com/url?sa=t&source=web&rct=j&url=https://engineering.careers360.com/articles/jee-main-eligibility-criteria/amp&ved=2ahUKEwiQv9S24cTrAhUUbn0KHUZnC4QQFjAKegQIAxAB&usg=AOvVaw0Ddf__yVIUe0laa-JjEit-&cf=1
Hope it helps