Different styles of sidebars resulting in non-editable sidebar table of content

I have two documents opened in the same Pages window. On both I selected to view table of contents. However, for one document, the sidebar looks like this:

While for the other, it looks like this:

On 1st document above, I can click on Edit and change the levels I want to see in the list. But, for the 2nd document this is not possible, there is no Edit button.

I think this also relates to Table of contents not showing up in the … - Apple Community

existing question, specifically this comment Table of contents not showing up in the … - Apple Community

Resizing the sidebar width or changing the order of documents in the open tabs does not help.

So I guess the solution would be to have Pages show the same sidebar style for both documents.

Any ideas?

Thank you!