Hi, this is because the "View user list" permission set to "Members" only in a fresh install of Flaruim via the Admin CP under the Permissions tab.
You are also getting that style of error because you have debug mode enabled. Normally, users who are not able to see other user profiles with this permission set to exclude the group they are a part of would get "The page you requested could not be found." instead when debug mode is set to false
in your Flarum's config file.
Hope this answers your question! 🙂