Are you referring to the University of California system? If so, the only Academic Index I am aware of for the UC’s is ELC. ELC guarantees Freshman applicants a spot in a UC if the student is in the top 9% of their HS class or statewide. The default campus is UC Merced.
All UC transferable courses will be used in your UC GPA calculation (if taken summer after 10th grade through the summer prior to 12th) and no difference in weighting for Non-STEM vs. STEM.
Information on how the ELC is determined for local: Local guarantee (ELC) | UC Admissions
For Statewide: Statewide guarantee | UC Admissions
On the application review, each UC campus will weight the 13 areas of criteria differently but having a competitive GPA, good HS course rigor and solid Personal insight essays are the most important. None of the UC’s will disclose how they determine their admission scores.
Take the CC courses where you know you will excel since these grades will be on your permanent college transcript. Also if the HS offers AP classes of interest, take those over CC classes unless their is a schedule conflict. You are evaluated within the context of your HS so utilize your HS curriculum first then select CC courses of interest vs taking classes for the sake of college admissions.