Collapsed by default is not clickable

Collapse by default.png
Collapsed by default is not clickable

Found this on the Microsoft Community:

Make sure that your document is saved in the most recent file format. If the document is in compatibility mode, the feature may not work. To "upgrade" to the newest file format, click File | Info | Convert.

Click in a paragraph formatted in a built-in heading style. Press Ctrl+Shift+S to display the Apply Styles pane. Click the Modify button. In the dialog box, click the Format drop down and then click Paragraph. The "Collapsed by default" option should now be available.

Stefan Blom
Microsoft Word MVP
Volunteer Moderator
(MVP program information: https://mvp.microsoft.com/)

Worked for me.