Would you be required to mention your intended major in college/university applications?

Most colleges allow students to go 'undecided' into college, including ivys. The major you choose will have almost no role in your admission process and is mostly based on other stuff like the essays, your scores, interests, resume, the usual. But choosing a major won't do you any harm as you can still change for about a year or so.

yes you do, but you're not committing to anything when you fill it out, and most colleges will not require you to declare a major until sophomore or even junior year.

basically, there is a spot on the Common App (and pretty much all other applications) that ask you what you PLAN to major in, but for most schools that's not binding and just gives the admissions committee an idea of what you'd be interested in studying. that can affect how they look at your application, because they'll want to see links between what you say you're interested in studying and your activities, schoolwork, essays, etc. the only schools that do actually make you apply into a major as a freshman are the UCs and some other similar state schools, and that's specifically for high-interest majors like CS, engineering, etc.

I dont know about ivies as Im not interested in Ivies but typically you can apply as undecided in a specific college like undecided engineering and take 1st-year classes and narrow it down and if you think you want to do mechanical eng but you want to switch to civil eng thats almost always an option,