What’s her magnum opus?

I am not a swiftie but my sister is. I once tried starting a conversation with her about what Taylor’s magnum opus when it comes to her albums. Since my sister probably doesn’t like to talk to me (we have a complicated relationship) she said all of her albums or was just didn’t understand the question.

Now a magnum opus doesn’t have to be your personal favorite album but it’s her most important album. For example, my favorite band is Pink Floyd. While it’s debatable, many fans consider The Dark Side of the Moon to be their magnum opus even though albums like Wish You Were Here and Animals are considered better albums in the eyes of other fans. So what is Taylor Swift’s Dark Side of the Moon?