Should my essay be about what I want to study, and why, or have some sort of connection to it?
Not necessarily, it’s more about showing what kind of a person you are. My older son who was a computer nerd did end up writing about computers. My younger son (who was undecided but ended up majoring in Internation Relations) wrote about what he learned from origami. Both kids wrote their essays in a somewhat humorous way, which I think was as important as showing that they were self-starters who pursued interests outside of what they learned at school.