We're in the process of updating the documentation for Zotero 5.0. Some documentation may be outdated in the meantime. Thanks for your understanding.
What is the official Harvard style?
“Harvard style” is a popular name for the author-date type of parenthetical referencing.
This way of referencing does not originate from Harvard University1). There are many variants of “Harvard style” in use, and there is no “official” Harvard Style. You can check the many “Harvard” styles available in the Zotero Style Repository to see if there's one for your institution. If not, you can compare the options to the style guide of your institution or professional association to try to find the best match. If you're not able to find a good match and you believe your variant to be widely used, you can request a new style.