OP mentioned applying to an unspecified type of engineering. UCLA’s engineering division is more selective than its letters and science division. An unweighted HS GPA of 3.75 would not be very competitive in that context (and UCs tend to weight HS grades more than test scores).
On the UC application, students enter their courses and grades, then the computer calculates the GPAs used. The most commonly referred to HS GPA for UC purposes uses 10th-11th grade a-g course grades, with up to 8 semesters of +1 honors points (note that many HS honors courses are not listed as such for UC purposes, and OOS applicants can only use AP courses as honors courses). But there are also other GPAs shown to admission readers, including unweighted and weighted without the 8 semester limit.
The most common type of HS GPA for UC purposes tends to be about 0.3 to 0.4 higher than the unweighted 10th-11th grade a-g course GPA, if the student has taken lots of honors or AP courses.