This policy setting controls whether the specified Office application notifies users when unsigned application add-ins are loaded or silently disable such add-ins without notification. This policy setting only applies if you enable the 'Require that application add-ins are signed by Trusted Publisher' policy setting, which prevents users from changing this policy setting.
If you enable this policy setting, applications automatically disable unsigned add-ins without informing users.
If you disable this policy setting, if this application is configured to require that all add-ins be signed by a trusted publisher, any unsigned add-ins the application loads will be disabled and the application will display the Trust Bar at the top of the active window. The Trust Bar contains a message that informs users about the unsigned add-in.
If you do not configure this policy setting, the disable behavior applies, and in addition, users can configure this requirement themselves in the 'Add-ins' category of the Trust Center for the application.
Set the policy value for User Configuration >> Administrative Templates >> Microsoft Access 2016 >> Application Settings >> Security >> Trust Center 'Disable Trust Bar Notification for unsigned application add-ins and block them' to 'Enabled'.
The following resource is also helpful.
This security hardening control applies to the following category of controls within NIST 800-53: Configuration Management.This control applies to the following type of system Windows.