via Apple.com:

Apple offers Volume Purchase Programs and Apple Configurator on Mac to help enterprise environments manage and mass-deploy apps on iOS devices. But certain business partners might still need to use iTunes to install apps.
Install apps with iTunes

If you’ve already installed a newer version of iTunes, you can download this version of iTunes on your Mac, PC 32-bit or PC 64-bit* and run the installer. After installation is complete, you can continue to deploy apps with iTunes.
You won’t be prompted to download new versions of iTunes after you install this version. Learn how to update to the latest version of iTunes when you’re ready to upgrade manually.

A month ago, Apple released a new version of iTunes which removes iOS App installs and the App Store. iOS 11’s app store is the only place to discover and buy new apps. Even Apple’s iOS web-pages for apps are still up but the “view in iTunes” button is gone. 

I didn’t like this step. Break out the iOS App Store to a separate application or build it into the Mac App Store so I can view and purchase apps on a properly sized screen, not a constrained one such as an iPhone. The old iTunes also made restoring a phone much easier as apps were stored locally on my computer and wouldn’t be recovered from Apple every time I restore a phone from an iCloud Backup. Finally, for apps removed from the App Store (like ProTube), I could still restore applications I bought from my local copy as opposed to the awful experience of being told I could not restore ProTube on my iPhone 8 because it was no longer available on the App Store.

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Apple has back-tracked by releasing the old version of iTunes for customers who need it with a note here that you won’t be prompted to update iTunes if you’re running this version. This is nice for those who need it but kind of crazy for Apple to do. It shows a lack of foresight into the needs of the customers and this is not a fix, it’s merely Apple telling us to keep running iTunes as it was and miss out on future updates as a result of needing a feature no longer supported.

Despite the fact I miss the functionality, I won’t run an iTunes version that will eventually break with future OS updates just so I can have a feature that officially Apple no longer supports. 

It’s a nice gesture for people who absolutely need this feature and will keep a Mac mini with the current OS on it so they can continue loading iPhones in Volume Purchase programs without issue.