Using older versions of Outlook for Mac for personal email and calendar
Yes, they've not only done it to us, either. At work I have to use MS Windows laptop with MS Office and they've just repositioned all the buttons (for calendar, favourites, tasks, etc) to the top left side. No choice to switch back. Just because MS think it's an improvement didn't mean the whole world should have to go along with it. We should have s choice
Applicable to Outlook Windows only and off-topic for the Outlook Mac discussion, but we just went through this at work also. You can move the buttons from the sidebar back to below the folder list.
Go to Options, Advanced, and un-tick the box which says 'show apps in Outlook.' Restart Outlook when prompted and you should see the sidebar disappear and the navigation buttons will return to the bottom of the panel.