If I take online courses on coursera or another platform, will this count towards the coursework section of my profile?

I agree with @DebaterMAX. In general, as long as you have taken the most challenging courses at your school, you should be fine. I heard that some elite colleges have a part where your guidance counselor would sign to prove that you have taken the most rigorous courses. So it probably won’t affect your chances of admission. However, this might put you at a disadvantage in college. But something you can do is to self-study APs and take the exam. This would make your academic profile look stronger.

No it doesn’t count as coursework more like achievements/awards and ECs for doing stuff with the knowledge. Also the rigor/class work depends on high school if you have no advanced classes it shouldn’t be held against you as colleges will know you did what you could have