AP Capstone is not a single course but a programme of two, and structurally it is the most different item in the AP catalogue.
AP Seminar
The first step. The student examines a topic from different perspectives, compares sources and builds an argument.
Assessment combines team work, an individual paper and presentation, and an end of year exam. So the grade is not tied to a single day.
AP Research
The second step, and it requires Seminar to be completed. The student sets their own research question, carries it out across a year and submits an academic paper and a presentation.
This is genuine independent research at school level and resembles the IB Extended Essay.
What it gives
It demonstrates directly the skill universities expect: evaluating sources, building an argument, academic writing and defending it.
When both are completed and four additional AP exams are taken, a separate certificate is awarded. Its name and conditions are on the College Board's own pages.
Its limit
The school has to offer the programme; it cannot be taken from outside. The number of schools offering it in Turkey is limited.
The course content also gives no subject knowledge; it teaches method. It is not read as preparation for a particular university department.
Who should take it
Students who enjoy research and whose school offers the programme. Also students whose exam performance fluctuates but who work well over a long stretch, since assessment is not tied to a single day.