it depends on the college and whether or not that is an “impacted major”…
For example, at our local public college, many students want to be Bio majors as this is an excellent value college for Pre-meds. But we can’t have half the class being bio majors…so they make you declare what your major will be and limit how many of certain majors there will be and it is difficult to switch majors.
other colleges have a Single-door admissions policy and don’t require you to declare what you want to major in…and you can switch at any time (assuming you are prepared).