Congratulations on a wonderful profile.
UCSB also admits to the university first and then the major.
Regarding the UCSB comment, that is true for the College of Letters and Sciences but for Engineering, the college admits by major. If you are not admitted into CS and you list a major in the College of L&S, then you will be considered for your alternate.
The UC admission by discipline has 2024 admission data listed. I have only found 2 campuses with updated 2025 admission data so I will list them below:
UCLA: Number of CS applicants: 6,806
Admit rate: 7.3%
Admitted Weighted GPA (25-75th percentile) 4.64- 4.92
UCI admit rate for SE was 28.6% and Game Design was 13.7%. UCI admits by major and will consider your alternate major.
I would also group UC Davis into the tossup category with UCSB, UCI and UCSD.
Best of luck.