Based on your description, you would like to make an outline with collapsible headings in Word for Mac which is not supported on Mac currently.
I have done some research and found the following threads.
Office 365 for Mac: Expanding/Collapsing headings in Word
Expand/Collapse Headers with Word 2016 for Mac
2 Smart Ways to Collapse or Expand Parts of Your Word Document
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As a workaround, maybe it can be realized with VBA code.
Since tag "office-for-mac-itpro" focuses on general issues about Microsoft Office for Mac.
I will modify the tag to be “office-vba-dev” to get related help.
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