“How do undecided students stand out from other ‘decided’ students who showed a clear passion?”
I see two ideas in your post. First, is the easier one—does listing a major as being undecided help or hurt. Second, how does a student without showing a clear passion stand out. I think the first has been answered here. The second is another routine question on CC. Short answer, there is no magic answer or solution here.
Some students, a minority in my opinion, are “decided”. I daresay every college, unless they lock you in, understands that a proposed major or field of study is aspirational at best.
As for passion, I think this is a concept that is easily misunderstood from a student’s perspective. If you analyze just one individual, on one level, you can try to identify that person’s passion. Flip this around, and if you are a college and building a cohort or class of hundreds to thousands, you want a diverse, vibrant community of students.
This “passion” concept, as applied only to college applications, makes an individual try to develop interests just to appeal somehow to the ad coms building a class in the hopes that you will be one of the accepted to X, or Y, or Z university. This is all wrong. Utilitarian and understandable but wrong.
“Passion” is better understood as developing who you are, what you like, what is special about you. It’s not about an end game for college applications. So, if what you like is writing poetry, go forth and write. I know students who applied as being passionate about poetry who are in engineering and pre-med programs (and not English majors). Your “passion” does not equal major. It’s just what drives you. It can be soccer. It can be academic team. Science fairs. Dance. Music. Theater. Rap. Comedy. Farming. Art. Environmentalism. Activism. Empathy. Anything. It can be a combination of two, or three, or more of these. It can be a highly specific thing in one. There is no magical formula. There is just you being you.
Of course, schools would like to see you developing an interest in something or some things. This is how they see how you might benefit the school. If you are a jack-of-all-trades, if you dabble, it indeed can be hard to stand out. But it’s not about “decided” students. Students that stand out have just invested time in doing things they like. It’s not a gimmick. The more interested they are in some area, they more they choose to focus on that area over another. Over time, they have something that makes them stand out. Equally, a student might start out as passionate about A and B activities, but over time, A wanes, B remains constant, and new activities C and D become dominant. That’s growing up. But it’s also about growing. It humanizes you too.
If you are indeed more of the jack-of-all-trades type, or more middle of the pack while being an awesome high-achieving student, how do you stand out without such an interest or focus? Short answer? Write fantastic application essays. Choose teachers who will write fantastic letters of recommendation. Long answer: go be you.