I sent all my SAT scores to UC Davis. Is the portal only supposed to show the highest reported score

You don’t need to send your scores to all of the UCs. Send it to one and they will be shared with the others. Is your the score posted on the UCD portal your highest score from a single setting?

Read here: http://admission.universityofcalifornia.edu/freshman/requirements/examination-requirement/index.html

Report ACT and/or SAT scores on your admissions application, then request that an official copy of the scores be sent to us from the testing agency. You can have your official score report sent to one UC campus, and all campuses you apply to will receive it.

For the SAT with Essay, we will focus on the highest total score from a single test date.