iTunes 12.4 just arrived with the latest Mac OS update (10.11.5) and it adds the sidebar back.
1/ Where is this sidebar? Once you’ve updated iTunes to the latest version, you can click on the View menu at the top of your screen and choose Show Sidebar. Instead of the icons, you now have a drop-down near the top-left of iTunes’ window, from which you’ll select the type of media you want to view. To change what you’re looking at, pick a different option from there.
2/ Edit the media types — If you only need a few of those media types to show up, pick Edit Menu from that list then turn off the media you don’t ever use.For example, we don’t get TV shows via iTunes here anyway.
3/ Edit the Sidebar — With iTunes 12.4, you can also switch up what’s showing on the new sidebar. To do that, hover over where it says Library and click the Edit button that appears. Select or deselect as your heart desires. (These options change depending on what media type you’re configuring.)
When you’re finished, click Done in the upper-right corner.
4/ Visual changes — If you have been using the Heart button to tell iTunes which tracks you like best so you receive better music recommendations, it only appeared when you hovered your cursor above the track name. Now it’s an ever-apparent heart shape beside the now playing section at the top centre of iTunes. There are two ways to sort a current view: in the iTunes Menu Bar there’s the View>Sort By drop down menu, or you can have them always available on-screen using View>Show View Options (or Hide View Options). Up Next is easier too – the Up Next and AirPlay speakers operators are now much easier to find with their own dedicated buttons on the iTunes toolbar, to the right of the media description.
5/ New features — It’s now much easier to set shuffle or loop commands on tracks and you can see small icons denoting the status visible in the media description/playback in the iTunes menu bar. The Music, Movies, TV Shows, Podcasts, and other media items section at the top left of iTunes has been changed: now you don’t see the most popular items lined up beside each other, but you get a pop-up menu to help you navigate between media types. You can also edit these so you only see the fields you most frequently use.
The Forward and Back buttons at top right in iTunes now help you jump directly between pages you’ve been browsing, just like in a proper browser. This also means you can shift between Apple Music, your music, Movies and so on.