User Configuration > Administrative Templates > Microsoft Word 2016 > Word Options > Advanced
User
HKCU\software\policies\microsoft\office\16.0\word\options
This policy setting allows you to specify the minimum zoom level percentage at which point the expand/collapse on-object UI stops rendering. Regardless of the value specified for this policy setting, the expand / collapse feature is still available from the context menu for headings. If you enable this policy setting, you can specify a minimum zoom level percentage from 0-500. If you disable or do not configure this policy setting, the minimum zoom level is set to 50%.