suppose I get my board Mark's % in 2020 and I try for iist in 2022 after giving the jee advance then will they accept me with 2020 board marks and jee advanced score of 2022
Yes, of course you can apply. See JEE-Advance has two consecutive attempts so if you are passing out from your 10+2 in 2020, then you are eligible to give JEE-Advanced at most upto 2022 and after that you will not be eligible. So if you want IIST then you can appear in JEE-Advance 2020 and your 12th result of 2020 will be considered.
For more details refer to the link given below :-
I hope this information helps you.