No one has offered this solution yet:
I also had the problem where the "View" menu did not have a "Show Sidebar" option, and there was NO pull-down menu in the upper left (not "apps", not "music" -- no menu at all). The problem, as said earlier, is that I was 'looking at my iPhone'. I.e., topics listed at the top center were: "Summary", "Info", "Apps", "Music", etc., and I had already clicked on "Apps", which is not the thing to do (unfortunately). There is no pathway from the "Apps" option for the iPhone section to actual App updates (sigh!). Solution:
1. If you can't find the "Show Sidebar" option in the "View" menu and don't see any pull-down menu at upper left, click on the blue "DONE" button in the upper right.
2. This should get you back to your library, and now be able to see the pull-down menu at upper left and see the "Show Sidebar" option in the "View" menu.
a. If you do "Show Sidebar", the page will look a lot like earlier (better) versions of iTunes, and you can click on the "Apps" line near upper-left.
b. If you go to the pull-down menu, instead, you get the same 4 choices that are in the sidebar ("Music", "Movies", "TV Shows", and "Apps"). Clicking on "Apps" gives you the Apps page, with any available updates mentioned at lower left.