Policy
Set the maximum zoom level for expand / collapse on-object UI
This policy setting allows you to specify the maximum 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 maximum zoom level percentage from 0-500. If you specify a value of 0, the on-object UI never renders. If you disable or do not configure this policy setting, there will be no maximum.
24fc13ed659f L_ExpandCollapseUIMaximumZoomLevel Registry
Copy registry mappings
HKCU\software\policies\microsoft\office\16.0\word\options\maxeczoom Policy notes
This policy setting allows you to specify the maximum 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 maximum zoom level percentage from 0-500. If you specify a value of 0, the on-object UI never renders. If you disable or do not configure this policy setting, there will be no maximum.