Bug in Chicago 17 CSL
When an old-fashioned long title has two components joined by “or”, the “or” should not be capitalized. See CMOS 17 14.91. But text formatted with the production Chicago 17 CSL has the "or" capitalized.
For example, my book has this title
Logic made easy: or A short view of the Aristotelic system of reasoning, and its application to literature, science, and the general improvement of the mind
but it gets formatted as
Logic Made Easy: Or A Short View of the Aristotelic System of Reasoning, and Its Application to Literature, Science, and the General Improvement of the Mind
For example, my book has this title
Logic made easy: or A short view of the Aristotelic system of reasoning, and its application to literature, science, and the general improvement of the mind
but it gets formatted as
Logic Made Easy: Or A Short View of the Aristotelic System of Reasoning, and Its Application to Literature, Science, and the General Improvement of the Mind
In either case, even if Chicago would want a lowercase "or" after a colon there, I don't really see how we can reasonably automate that (subtitles can also start with an or, which should then be capitalized). If you are really set on keeping the title as is, you can apply the no case HTML tag as described here: https://www.zotero.org/support/kb/rich_text_bibliography
That makes sense. I’ll just change colon to comma or use class="nocase".