I finally opened a support ticket because this issue seemed to be unresolvable by the user, which turned out to be the case. They replied saying that this was a known issue caused by a MacOS Sonoma update. A fix is in the works. In the meantime, I’ll leave the workaround here for posterity.
- Open the style file for editing (Tools…Output Styles…Edit).
- Navigate to the Footnote/Bibliography/Citation section and select Template.
- Click on the “Reference Types” dropdown menu and choose the relevant reference type for editing.
- The cursor will automatically be moved to the correct reference type editing window.