There are three types of courses:
The first is the elective course.
If you have interest or skill in any subject, you can choose it.
For example, Link, who is better at biochemistry and potions, can choose related courses for learning.
For instance, Link's newly upgraded "Alchemy Specialization" talent, combined with the "Material Specialization" talent, is enough to make him a decent alchemist, and he can select the corresponding courses.
There are no thresholds, no high requirements, as long as you opt for, you will be able to learn.
The second is the advancement course.
For these courses, you cannot listen just by choosing them, you must pass an exam.
You need to have a certain foundation and satisfy the learning requirements before you can learn.
The third is private tutoring by a mentor.
These are the most special. You must first have a mentor who is willing to take you as a student.