Not all UC campuses admit by major.
For UCB, Psychology is a High Demand Major so you need to list Psychology as your first choice major for the best chance to pursue that major.
https://ls.berkeley.edu/ls-high-demand-majors-first-year-students
For UCLA, UCSB and UCD, Psychology is in the College of Letters and Sciences which does not admit by major so you can still select Psychology as your major. No advantage if you select Undeclared.
For UCSD and UCI they admit by major and will consider an alternate major so you can be admitted into your Primary major, alternate major and sometimes Undeclared
UCSC admits into a “ proposed” major which is similar to Undeclared since you need to take pre-req courses before you can declare.
UCR and UCM admit by major, will consider an alternate major and changing majors later is not too difficult. This is very dependent upon which major you may switch into especially CS or Engineering.
My advice is to apply to the major you want to study.