Chicago short notes including subtitles

I'm using Chicago Manual of Style 17th edition (note). From the manual itself and Zotero's description (https://www.zotero.org/styles?q=chicago), it seems like only the main titles of books and articles should be included (the material before the colon).

But in my notes, I'm almost always getting the full title, including the subtitle. For example, I have a note that reads
Sills, The Volunteers: Means and Ends in a National Organization
instead of just
Sills, The Volunteers

Does anyone know how to get just the short version?
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