Regarding appearing in the JEE advanced, you are to appear for the exam twice and the attempt would be counted from the year you have given your X11 board exams.

So, reagrding your case, you have given your board in 2018, so you are allowed to give in 2109 and not allowed in 2020 to appear.

Thank You

hello candidate 

as you have given two attempts of jee advanced you are not eligibile for jee advanced 2020 as maximum attempts for jee advanced are two and jee mains are three including your 12th year irrespective of whether you give it or not.

therefore even if you do not qualify your attempt is counted

hope this answer helps

For appearing in advance you need to first clear paper of mains this year too. Its not valid to be eligible directly into the advanced section , so you need to first clear the first round that is mains this year too and as a next step you would be able to appear in the advance.