How to narrow down a field of study when you enjoy and perform well in every subject? Might it be odd for a student to love and have excellent academic performance in all subjects—I am that student. I am really confused what to study in the university. My grades are similar (high) in all subjects, and I prefer both scientific and non-scientific subjects. It's like I want to get a degree in all fields. How can I decide what I should choose? What can I study? I have tried a lot of tests, even paid ones, but I get similar percentages for all choices.
Performing well in every subject is simply impossible past the high school level.  Conversely, I would argue that a strong high school student in a US-style system should be able to perform acceptably in every subject (excepting effects of disabilities), since studies in high school are typically designed to give the sort of general grounding that will be required in most professional careers (critical thinking, analysis of written ideas, clear exposition of your own thoughts, creative expression, foundational mathematical and scientific knowledge).

Beyond high school, one might still have the potential to be good at any particular thing.  It is just that this is the time when one begins to study specialities more deeply, and there are simply too many of them to be an expert in all of them.  This happens in a fractal manner at each level: in undergraduate, you can be excellent at whole major, but cannot study all the majors; in graduate school, you can be excellent at a sub-discipline, but cannot study all sub-disciplines; as you establish a career as an academic, it is important to identify a small scope of contributions within the disciplines you work where you can contribute uniquely well.

These realities also imply an answer to your dilemma.  You don't have to pick the "right" academic focus, you just have to pick one that you will enjoy.  And you can even afford to be wrong a couple of times, as long as you figure it out and shift to something that suits you better.  Moreover, it's possible to do this at every level (though it's harder to make large shifts the deeper you go), undergraduate, graduate, postdoctoral, and even beyond.

In short, you can think of academic areas like the Tim Minchin love song says: "If I didn't have you, someone else would do."