User Configuration > Administrative Templates > Microsoft Excel 2016 > Excel Options > Security > Trust Center > File Block Settings
User
HKCU\software\policies\microsoft\office\16.0\excel\security\fileblock
This setting determines whether Trust Center settings for blocking load of potentially unsecure workbooks applies to those accessed by external links. If you enable this policy setting, external links to workbooks that are blocked by File Block settings in Trust Center will not refresh. Attempts to create new links or refresh data from blocked workbooks may result in errors. If you disable this policy setting, attempts to access external links data will not be subject to File Block settings in Trust Center.