Earlier this year MS (dis)"improved" OneNote out of Office and into Windows 10.
One of the "improvements" (you can see the sarcasm dripping from that word, right?) in the Win10 version is that note files can ONLY be stored in OneDrive (you can imagine what the conspiracy theorists say about that ...) . Another "improvement"
is that many of the features in the Office version have not been ported into the Windows 10 version, "yet". Who needs all of those pesky features cluttering up the program ...
You have 2 options.
One is to install the Office 2016 version of OneNote and keep using it. But MS no longer will be adding new features to it, and it has a definite end of life at some indefinite date in the future ...
The other option is to import your old notes into the new version.
https://www.onmsft.com/news/heres-how-to-move-your-onenote-2016-local-notebooks-to-onedrive-a-new-feature
If you still prefer to use OneNote 2016 over the new OneNote UWP app, Microsoft
announced some bad news yesterday. Later this year, OneNote for Windows 10 will replace OneNote desktop in Office 2019 and become the most up-to-date version of OneNote.
OneNote 2016 will remain available and be supported through October 2025, but it will no longer receive new features going forward. However, you may continue to use the legacy app if you still need some of its features, such as the ability to store notebooks
on your local hard drive instead of the cloud.
If you do use local notebooks and want to make the transition from OneNote 2016 to OneNote for Windows 10 though, the process isn’t exactly intuitive. OneNote for Windows 10 only supports notebooks that are stored on OneDrive, OneDrive for Business or SharePoint,
and you can’t use it to open local notebooks. But as noted by OneNote MVP Marjolein Hoekstra (who is behind the OneNote Central Twitter account), OneNote for Windows 10 can now move local notebooks to OneDrive for you. This is apparently a new feature that
quietly rolled out last week:
No matter what version of OneNote you use, you can download a copy of any of your OneNote notebooks to your PC or Mac — either as a backup or to upload its contents to another account.
Note: Exporting and importing notebooks through OneNote Online is only available for notebooks stored on personal OneDrive accounts, not for notebooks stored on OneDrive for Business / Education or SharePoint. For
information about exporting notebooks to PDF files from OneNote 2016 for Windows, see
Export notes from OneNote as a PDF.
https://support.office.com/en-us/article/move-onenote-notebooks-from-your-computer-to-onedrive-b43692ae-ce27-4ab9-a8ad-a2aed225e6a5
https://techcommunity.microsoft.com/t5/blogs/blogarticleprintpage/blog-id/Office365Blog/article-id/419
We’re incredibly lucky to have millions of passionate OneNote users around the globe, and we love learning how we can help you remember, think, and organize better. In spending time with you, we heard a recurring theme: you want a single version of OneNote
on Windows that combines all the benefits of the modern Windows 10 app with the depth and breadth of capabilities in the older OneNote 2016. We took that feedback to heart, and over the last few years we’ve been focused on making OneNote for Windows 10 the
best version of OneNote on Windows.
Beginning with the launch of Office 2019 later this year, OneNote for Windows 10 will replace OneNote 2016 as the default OneNote experience for both Office 365 and Office 2019. Why OneNote for Windows 10? The app has improved performance and reliability,
and it’s powered by a brand new sync engine (which we’re also bringing to web, Mac, iOS, and Android). You don’t need to worry about being on the latest version since it’s always up-to-date via the Microsoft Store, and it lets us deliver updates faster than
ever before. In fact, over the last year and a half we've added more than 100 of your favorite OneNote 2016 features based on your feedback (thank you!), with more improvements on the way including tags and better integration with Office documents.
We’d love for you to start using OneNote for Windows 10 today, however we know some of you might not be ready yet. Maybe you rely on a feature we don’t yet support on Windows 10 (please let us know using the
Feedback Hub), or you don’t want to store your notebooks in the cloud. If so, you’re more than welcome to continue using OneNote 2016.
https://support.office.com/en-us/article/onenote-2016-is-missing-after-installing-office-2019-or-office-365-1844ba87-7248-4bd8-a735-66a52f98e6e5
After installing Microsoft Office 2019 or Office 365 on a PC running any edition of Windows 10, OneNote 2016 appears to be missing from the list of installed desktop applications.