Answering the WHY'S essaysAnswered
If I have an interest in a program e.g. sustainability, which I did not select as one of my academic interests on common app but have participated in it as an extracurricular, can I write about it in the "Why this school essay" if they offer a special program on it(but not as a major)?
Yes, of course! The why essay is for listing out what your interests are and how attending the college will help you achieve any goals related to them. If this is a genuine interest, you can write about how you will use the college's opportunities concerning that interest to your benefit. This will boost your essay as they usually want to know more that just your academic interests for attending that school.