junior, dual-enrollment program
If you do not know what you wish to major in, that is perfectly fine and no colleges would penalize you unless you applied to a specialized school and had no clue. If you apply to the Culinary Institute of America or Caltech and don't really want to pursue being a chef or having a STEM focus, well your are applying to the wrong school.
If I'm not mistaken, almost all the Top schools will not penalize you if you do not declare a major. However, keep in mind, you don't want to apply to the Wharton School at UPenn if you can't articulate why they should give you a spot when everyone else knows they are the top undergraduate business school in America and what they want to do there. That being said I have a few bits of advice.
1.) Do some serious research about colleges and find out when they expect you to declare a major. For instance at Brown, there is no core curriculum and you are supposed to dabble and experiment during your entire Freshman year and don't have to declare a major until the 2nd semester of Sophomore year. At which time you can declare a single concentration or a double concentration like Neuroscience and Film. They do not have to be related.
2.) Consider applying to Liberal Arts Colleges because their whole path of learning is to evolve you into your best person but having you delve deeper into being a critical thinker, a better writer, having deeper exposure to philosophy, science, languages, and fine arts. Schools like Pomona, CMC, Williams, Amherst, Vassar, Hamilton, Colgate, Haverford, Swarthmore are all excellent stepping stones to applying to Professional programs like Architecture school, Medical or Law school, or others. While you will be expected to pick a major, often you don't have to declare one until the middle of your 2nd year.
3.) Do not pick a major because your parents want you to be something or you think it makes the most money. If you are not careful, you will get what you asked for and not be happy with your choice. It's kind of like making reservations at a Michelin 3 star restaurant in Paris and walking in blind without doing your research. You might think something sounds great and find out it's the calves liver or other organs. It's much better to buy a book and figure out what they are famous for and have an outline prepared for all your courses in your meal. If you don't know what wine to pair them with, well they have specialized Sommeliers who are licensed and trained to help you pick wines that work best with your selections.
4.) Keep in mind that some majors are highly oversubscribed at certain schools so you need to flexible and strategic about picking a major. For example, do not assume that you will get into Stanford as a CS major even if you have perfect grades and test scores because that is the #1 major applicants declare. It might be better to pick one of the least popular majors at Stanford like Women's' Studies or Linguistics something that graduates less than 3% of the admits. Why? That will stack the odds in your favor that you get in. If you don't like your major after 1 year, you can often switch without much difficulty once you are already a matriculated student. But if you pre-determined a major, you should have a resume or C.V. that supports why you picked that major in the first place. So be careful, since college admissions officers are very smart and can easily connect the dots if you are just trying to find the side door in versus being upfront and walking through the front door.
5.) Since you are a junior, narrow down your top 3 or 4 possible majors. Then ask your friends and family if they know anyone that does these jobs. Chances are they do or know someone that does. Then ask them for their contact information and write to them and ask if you can have a Zoom or Facetime call with them to learn more. Have your 10 questions ready to ask them. If 1 or 2 really interest you, then ask them if you can job shadow them for a day. Sometimes they will be flattered and happy, other times you may have to ask someone else. But you need to see up close and personal what they do to see if you are really interested in the work.
Good luck.
To keep this community safe and supportive:
Thanks so much for the detailed response! I think I'm interested in health sciences, engineering, and computer sciences but I'm not sure how I can shadow a doctor due to covid. Any advice?