Onenote - Move tabs from top to side

Microsoft has actually decided to continue updating OneNote 2016: https://techcommunity.microsoft.com/t5/office-365-blog/your-onenote/ba-p/954922

OneNote 2016 still has many features that are missing from OneNote for Windows 10, like add-in support, ribbon customization, autocorrect rules, and it takes fewer clicks to get many things done. It's better for use with mouse and keyboard, while OneNote for Windows 10 is better for touch and pen. New features they have added over the last year or two, such as dark mode, phrase search and the note feed have been added to both apps.

I don't think you can have the sections not be displayed across the top, but you can pin the notebook pane to the left side of the OneNote window by clicking the pin button in the top right corner of the notebook list, and then you can expand the notebooks and section groups to see the sections on the side. You can also tick "Page tabs appear on the left" under File → Options → Display.