I believe that Zotero might have APA styles that can do this automatically. If not in the repository, you can get advice from CSL experts on how to make your own version with italics. [Editing the style might be simple or trivial.] However, APA's own guidance suggests that the italics are not essential and are, perhaps, deprecated:
https://apastyle.apa.org/style-grammar-guidelines/citations/basic-principles/author-date

Indeed, as I scan the repository examples for APA 7 styles I see none have an italics
"et al." option.

https://www.zotero.org/styles?q=apa

@adamsmith @damnation

edit: Why could you not do a search and replace with your completed document? Even if you must manually change the font/face style from the Word format ribbon this should only require a few minutes.

[[[ Don't do anything that might flatten your Zotero citation codes.]]]

edit2:
In anticipation of an argument I'll say that several professors at my university insist that, the style guide notwithstanding, et al. should always be in italics because it is not an English word. I'm certainly not suggesting that I agree with that view but I accept that the practice follows some rules.
[ https://canvas.hull.ac.uk/courses/213/pages/italics ]

However, note that even in the linked-to rules; et al. is NOT italicized because of the common use exception.

Many, many years ago I was dinged for not following the last mentioned example --italics-within-italics. That was back when reports were typed with a typewriter and italicized text was underlined. It has been more than 50 years and I'm still annoyed by that memory. I was required to use the Campball Guide which was essentially Chicago.