Mains marks has nothing to do with this. JEE advance marks are considered for the admission in IIST.

Basically Advance question pattern is not fixes so i am considering previous year cutoffs with previous year pattern.

For general category you need a minimum of 35% in JEE advance to get Aerospace or Electronics and Communication.

If you are from ST category then you can get at 11% of jee advance.

You can check this article for more information.

https://engineering.careers360.com/articles/iist-btech-cutoff