I don't want to use the "app" for OneNote that comes with Win10 - and in fact have removed it (see powershell removal instructions here). But when I want to choose OneNote 2016, not OneNote Online, to open a notebook on our (hosted on O365) SharePoint - it goes to the AppStore and gives me no other option. Yes, once I get it the first time by going dumpster diving through the file explorer and it is cached in OneNote client application I can still get to it, but that is very frustrating for training multitudes of new users. Any solutions? The library holding the notebooks is already set to force the client application as default.
Uninstalling the app is an optional step here. It is important to change the default version in Windows 10 from the App to the Desktop-Application.
It is not the best solution, as "normal" users won't get this change done. This article describes how to apply the change via GPO or SCCM.