FROM COMMON APP WEBSITE: That is correct, only classes that award high school credit should be inputted in the "Current Classes" section. The student may elaborate on non-high school credit courses in the "Additional Information" prompt within the "Writing" section of the Common App tab.
How to add in IB exams and Should I add my SAT or ACT tests here? If you add your SAT/ACT, you need to send them through College Board and/or ACT
How to add in Courses & Grades on Common App (updated Sept 2022)
FROM COMMON APP WEBSITE: When high school students simultaneously take college courses through a college or university, this is known as dual enrollment. For Courses & Grades, only courses receiving high school credit (i.e. appearing on your high school transcript) should be reported in this section. If you are not receiving high school credit for the course, you do not need to report this course in Courses & Grades.
How to report a college concurrent enrollment course (updated Sept 2022)
How to add a summer school or middle school math course (updated Sept 2022)
How to request "Other Recommender" Letter on Common App and Naviance