Heading styles are often set as "linked" styles rather than paragraph.




Display your Styles Pane (launcher in bottom right corner of styles dialog).
In the bottom of the pane, check the box to disable linked styles.





Click in the problem paragraph in the body and apply the style. Do not select text.
Update your Table of Contents.

Hi,

Unfortunately, Word on the mac doesn't have unlink style checkbox. However, I move document and tried unlinking on a PC and it didn't help. I share the content of the document and as it is confidential.

Ben.

If you can reproduce the problem in a document where you have replaced any confidential text with nonsense, you can attach that modified document here.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional