This article explains how it is possible for admins to view pages with restricted visibility as a participant.
Admins automatically have the right to view all pages in a workspace.
Some pages require more strict visibility settings, and in those cases view as participant might not work as the admin user has the right to view the page because he/she is an admin, not because they have been added to the allowed users' list.
So when the admin wants to view these restricted pages as participant, it is advised to add the admin as one of the allowed users. This way the admin has the rights to view the page even as participant.