User Configuration > Administrative Templates > Microsoft Outlook 2016 > Account Settings > SharePoint Lists
User
HKCU\software\policies\microsoft\office\16.0\outlook\options\wss
This policy setting allows you to prevent access to Microsoft SharePoint Foundation with Outlook. If you enable this policy setting, user profiles will not be able to upload new items or sync changes to the SharePoint list from the server; however, user profiles that have pre-existing SharePoint lists will retain their local data. In addition, new SharePoint lists cannot be connected when this policy setting is enabled. This can be toggled on and off to restore synchronization to existing lists. Note that users will not receive a message if synchronization has been prevented. If you disable or do not configure this policy setting, Microsoft SharePoint Foundation access will be allowed with Outlook.