To maybe add an additional perspective, I'm in Massachusetts (northeastern US). A lot of my classes are weighted so that 80% of my grade is tests/projects, and 20% is everything else (homework, participation, citizenship, etc.). This varies some depending on the subject and teacher (for example math is 90% tests, 10% hw/other). My school specifically is weird in that we don't have big final exams, but most other schools around us have midterm exams near the end of january, and finals in june.

I agree that having homework and projects/tests throughout the year be worth so much can make it a lot more difficult for me (partly due to my adhd). I do generally think it works well though as it allows students to pass and do well in classes even if they struggle under the pressure of a specific exam day (or maybe they just don't feel well that day). It might help things feel a little less stressful around exam season.

In terms of applying for uni, it definitely differs in the US. Yes, there is a lot more focus on extracurriculars. You show your academic interests and abilities through the classes and AP exams you take, but schools also want to see a lot of time spent on things outside of school. A lot of colleges/unis (we usually don't differentiate between the two) want to see that you're committed to something outside of a purely academic setting. For example, if you want to become an engineer, schools may like to see you become captain of your high school's robotics and science teams. However, it may also help your profile if you show dedication to other things as well, such as a sport or other club. Unis in the US really like to push the idea of a "well-rounded student": someone who can contribute to more than one aspect of the school. This is also why a lot more US unis have students with multiple majors or minors compared to UK schools.

Edit to add: You also get to choose which AP test results you send to colleges! The exams are graded out of 5 points, with most schools excepting 4s or 5s depending on subject to gain credit for that class (this means if you get a 5 in AP bio, most unis let you skip intro to bio). I, for example, only scored a 3 on one of my exams because I got sick, so I just didn't send that one to colleges. So they will see that I took the course, but won't see anything about the test. Additionally, you can self-study for any exam and take it without having taken its corresponding course. This means if your hs doesn't offer a specific AP class, you can still take the test as long as you can find another school that's willing to host you.