There is no way to restrict content from an admin. If you don't want an admin to see the content then you have to ask yourself should they be an admin or maybe the content should not live in Confluence. This is a fundamental software design issue. If you set up your application such that admins could be restricted from certain content then it would be possible for that content to be in a state such that no one could access it and an admin could could not grant that right because they themselves did not have access. There are not plugins for doing what you want.
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