Applying Undecided adds another hurdle if CS is your ultimate goal since for schools like the UC’s, if you do not get a direct admit into the CS major, it maybe impossible to change majors later.
All the Cal states admit directly into the major and it is far easier to change out of CS then to change into CS.
For the UC’s, each campus admits differently for CS.
UCB EECS requires a direct admit. CS in the College of Letters and Sciences does not admit by major currently but you are required to take pre-req courses and maintain a specific GPA to then declare the CS major.
UCLA, UCSC, UCD, UCSB and UCR are direct admit into the major so you need to apply for CS. UCLA does not consider alternate majors. UCSC and UCR will consider alternate majors. UCD and UCSB will consider an alternate major when applying if the alternate major is not in the same discipline or in the same College ie. College of Engineering vs. College of Letters and Sciences.
UCSD and UCI admit into the University first and then into the major. UCSD will consider an alternate major if the alternate major is not capped/impacted. UCSD also will accept many students Undeclared/Undecided and then you have to go through a lottery system with pre-req courses and GPA requirements before declaring the CS major.
For Private Universities, usually they do not admit by major but may require to get admitted into a specific college such as Engineering to be able to study your choice major.
If CS is your choice, then apply for CS. Like I stated before, the school you attend for CS will not have as much impact on you being successful as taking advantage of all the resources/opportunities available at the school you end up attending.
Plenty of great CS schools in California where you are qualified and competitive so just apply widely, make sure all are affordable and you have at least one safety school where you are willing to attend no matter what.
My younger son only wanted CS, wanted to stay in California so he focused on a few UC’s and several Cal states where he could get a direct admit.