See this year the JEE MAINS eligibility criteria of 75% is eradicated due to corona pandemic. SO you can go for the JEE MAINS 2021 without attempting for reexamination. You can use this chance.

Now if you don't want it and want to give JEE MAINS in 2022 then you will be eligible for 3 consecutive attempt i.e., JEE MAINS 2022, JEE MAINS 2023 and JEE MAINS 2024. If you qualify then you will be eligible for JEE ADVANCED and you can apply for two consecutive attempts.

I hope this answer helps. All the very best for your future endeavors!