As of 2020, among the top ten ban reason of the most commonly banned books in USA, which one was on the top?

WeeverBeezle, I understand your point, however there has most definitely been a huge campaign by interest groups to ban books from libraries and school curriculum. Watch the news once in a while.

There are no banned books in America. If book exists, and a copy is for sale, there is no law anywhere in the US that prevents you from buying it.