OK, so you are referring to the text formatted in the "TOC Heading" style. It does not show up in table of contents by default, as you have noticed. You can modify the style to include the desired outline level (in the Modify Style dialog box, click Format, Paragraph, and specify an "Outline level" on the Indents and Spacing tab). However, since tables of contents, by default, are based on outline levels, you would get a duplicate in the TOC of the text formatted in the "TOC Heading" style.

You could give the TOC Heading an outline level which would make it show up in the Navigation pane. However, if your TOC is based on outline levels (which is the default setting) you would see text formatted in the TOC Heading style in the TOC as well.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional