Apple has released iTunes 12.6.3 for those who need an App Store.
With the release of iTunes 12.7, Apple removed the built-in App Store; however, it has released iTunes 12.6.3 for those who still require the functionality.
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. 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.
How to downgrade to 12.6.3
1. Install 12.6.3
2. Launch iTunes it won't open just click on "Quit"
3. Navigate to: Music/iTunes and delete/remove file "iTunes Library.itl"
4. Navigate to: Music/iTunes/Previous iTunes Libraries and copy or move last "iTunes Library.itl" file from iTunes version 12.6 to previous location: Music/iTunes
5. Launch iTunes and you will be on 12.6.3 version
No it doesn't; just click the link on the official site link where it says,
"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." and it will work from there.
It's not so easy to do it coming from v. 12.7. You can install this version of iTunes 12.6.3 but can't be done straight from v. 12.7. You have to downgrade from 12.7 to 12.6 first and then install 12.6.3. Instructions on how to 'downgrade iTunes' are available on the official support site but take heed, it requires Terminal and sudo command line to delete the iTunes app, then replacing the iTunes Library.itl file from a previous version. Other wise iTunes will crash until above said measures have been taken.