iTunes 12.4 includes a redesigned interface that's designed to be simpler, with the reintroduction of a sidebar for easier navigation and a revamped media picker, as was shared by MacRumors earlier this month.
Today's update may also include safeguards to protect users from an issue that could cause music stored in iTunes to be deleted. The deletion problem affected a small number of users and while Apple was not able to recreate the bug, the company promised "additional safeguards."
The iTunes 12.4 update can be downloaded through the Software Update mechanism in the Mac App Store. Full release notes are below.
Now enjoy all of your music, movies, TV shows, podcasts, and more in a simpler design.
Navigation. Now you can use Back and Forward buttons as you navigate between your Library, Apple Music, iTunes Store, and more.
Media Picker. Easily switch between Music, Movies, TV shows and more--and Edit to choose just the items you want.
Library and Playlists. Use Sidebar to view your Library in new ways. Drag and drop songs to easily add them to Playlists. And Edit Sidebar to show only your favorite views.
Menus. Menus in iTuns are now simpler and easier to use. Use the View menu to customize your Library or try context menus to act on specific items.
http://www.macrumors.com/2016/05/16/...design-tweaks/