The provision as "unlisted app" means that the app cannot be found in the public app store.
Therefore, you can only invite your employees via the direct link.
Apple's terms of service state that an app in the public AppStore must be suitable for a wide audience. Employee apps, on the other hand, are designed for a specific group of users - the company's users. As a result, Apple typically blocks such apps during the review process and does not release them to the public AppStore. Apple introduced unlisted apps for this type of app in early 2022.