Policy
Set the minimum zoom level for expand / collapse on-object UI
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%.
7105bcb0fc18 L_ExpandCollapseUIMinimumZoomLevel Registry
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HKCU\software\policies\microsoft\office\16.0\word\options\mineczoom Policy notes
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%.