I know that Microsoft is phasing out of the 2016 OneNote and that if you have the tabs on the left it's not possible to move them to the top.
But some people in my organization still have the tabs on top version... which creates a confusion. First of all, do you know why some people still have this 2016 version in 2021 ?! And secondly, do you know how to change the tabs location from top to side ? Preferably within the app, and without having to download a new version of the app (because our organization members, outside of the IT team, do not have the possibility to install apps and softwares on their own).
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.