I do not think that I would take this as a freshman in high school.
One daughter took AP Music Theory. She liked the course a lot and got either an A or an A+ in it. However, it is a difficult course and was a lot of work. She is both probably the most talented musician that I have ever met, and a very strong student overall, and very strong at math.
In the first week of the class the teacher told the class that they would all hate her by the end of the year. This did not actually happen in my daughter’s case, but it was a tough class.
You will have time to take this later IMHO.