Would applying as undecided to Ivy league universities affect my chances of admission?

I want to add to @crsgo0422's answer a bit, because I think it's partially right but is missing some context.

Being undecided by itself will not disadvantage you applying to Ivies (or anywhere else for that matter). A large number of students apply undecided every year, and are admitted every year. But there are two different kinds of undecided—the kind where you're undecided between a couple of different subjects, and the kind where you have no idea what you want to do. The former is a better place to be in; the latter can be a disadvantage if you can't effectively answer questions like "what are your academic interests" or "why do you want to study the major you've indicated at this school." In a subjective process like this, being able to answer those questions effectively is crucial to standing out from other applicants to these schools.

What you really need to do is at least narrow yourself down to a couple of interests—less a giant list of options and more just a 2 to 3-pronged fork in the path in front of you. Then, it becomes less about you not knowing what you want to do and more about you using your first year or two of colleges to choose between a couple of appealing options.

So, that's all to say that it's not being undecided that inherently hurts you in the admissions process—it would theoretically be being unable to talk about what you want to study that could hurt you.

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