Yes, this is possible in WordPress using custom capabilities, user-specific permissions, or a membership/access-control plugin to restrict a page to one specific logged-in user.
WordPress Multisite doesn’t have a built-in “Log in as user” feature for Network Admins. The usual approach is to use a trusted user-switching plugin that supports Multisite, which lets an authorized admin switch into a user without needing their password and then switch back securely.
