jarn_19
As you have found, the Navigation pane can't see headings that are inside table cells. This is a known limitation with pane. You can send feedback to Microsoft using the feedback facility in your version of Word (see https://support.microsoft.com/en-gb/office/how-do-i-give-feedback-on-microsoft-365-2b102d44-b43f-4dd2-9ff4-23cf144cfb11).
If converting the table to text is a possibility, that would work around the issue. However, I am assuming that you are using tables for a reason, so getting rid of the tables may not be an option.