This policy setting controls whether users are taken to a custom menu tab when they choose the File menu in an Office app, such as Word or PowerPoint. A custom menu tab can be provided by an installed add-in.
By default, when users choose the File menu, they are taken to one of the File menu tabs provided by Office, such as Home or Info.
If you enable this policy setting, and an installed add-in provides a custom File menu tab, users will be taken to that custom tab when they choose the File menu.
If you disable or don't configure this policy setting, when users choose the File menu, users will be taken to one of the File menu tabs provided by Office, such as Home or Info.
Note: This policy setting only applies to subscription versions of Office, such as Microsoft 365 Apps for enterprise.