Hi @Richard Curtis,
Thank you for posting your question in the Microsoft Q&A forum.
According to your concern, you can create a Table of Contents using bookmarks via TOC field code. For example, I have the following bookmarks which is named as month1 and having contents like this:

To create toc for this bookmark, press Ctrl+F9 to insert Field Code and use the switch like this: {TOC \o "1-3" \h \b month1}
With these switches, the toc will show the contents within the bookmark month1, heading levels 1 to 3 and make those entries clickable.

You can find more guidelines about these switches in this article: Field codes: TOC (Table of Contents) field - Microsoft Support
I hope this information will be useful to you. Please follow these steps and let me know if it works. If you have any news about this issue, please do not hesitate to let me know.
Thank you for your patience and understanding. If you have any questions or need additional help, please feel free to ask them in the comments so that I can continue to support you.
Looking forward to your response.
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