Unlisted apps are on the way to the App Store, not that you’ll ever see them. Unlisted apps are exactly what they sound like - apps that should be undiscoverable in the App Store. But they’re there. iDownloadBlog explains, saying such apps are not for the general public, but will generally be distributed by administrators “through Apple’s Business Manager or School Manager.” Support for such is new, according to iDownloadBlog. It has Apple explaining to developers:
Your app may qualify for unlisted App Store distribution if it’s designed for a limited audience. Examples include apps for employees, apps for specific events, sales apps or research apps. Unlisted apps are distributed using a direct link to the app’s product page on the App Store, but they do not appear in App Store categories, search results or other App Store listings.
You may have caught the part where Apple said an app “may qualify” for unlisted status. “To publish an unlisted app on the App Store,” iDownloadBlog says, “developers must submit a request to Apple.” More info is available on Apple’s site.