NIT

Actually the eligibility criteria for NITs require minimum of 75% in 12th boards or being top 20 percentile in your respective boards.

The only exception is for SC/ST category who require a minimum of 65% in 12th boards.

The final conclusion is that you should have minimum of 75% in boards to be eligible to get admission in NITs regardless of JEE performance.

I have been trying hard to get the same question answered for the past one month. 
After a month and about 100 calls they said  "learner is not in top 20 percentile but did not tell the cut off marks. 
I am still trying to get that value because according to statistics until 2019 which NIOS provided to JOSAA 347/500 was the cut off for top 20 percentile. My son has 367 and still they say not in top 20

Here are the basic requirements 

• There is no age limit for JEE Main 2024 eligibility criteria for repeaters.
• He/She must have passed their class 12 exam in 2022, 2023 or 2024.
• Three consecutive attempts are allowed for the JEE Main 2024 examination.
• Students should have secured the minimum required qualification marks for JEE mains.
• Candidates should have taken at least 5 subjects for the class 12 or qualifying exam (Physics, Chemistry, and Mathematics mandatory).

Yes, you can use your 2023 rank card to get into NITS in 2024 as long you do not fail the above points.

You stand a good chance of being accepted into prestigious NITs. Candidates should aim for a JEE score of 250 in order to be admitted to NIT. A 90 percentile or higher can lead to admissions to prestigious NITs like NIT Delhi and NIT Calicut. Even lower ranks—70,000 and above—can get you into less well-known NITs, such the NITs in Sikkim and Meghalaya. 

No, it is not required to apply to every National Institute of Technology (NIT) for admission. Admission to NITs is primarily conducted through a centralized process managed by the Joint Seat Allocation Authority (JoSAA) based on the scores obtained in the Joint Entrance Examination (JEE) Main.