In early May at an education-focused event in New York City, Microsoft announced Windows 10 S, a version of the OS that only runs apps that are obtained through the Windows Store. Of course, this meant porting the entire Office 365 suite to the Store, and since the Surface Laptop - the first consumer PC with 10 S - began shipping, it was the only way to get Office from the Store.
But a couple of weeks ago, Microsoft began inviting Windows Insiders with Office 365 subscriptions to try it out. Those that have been selected can now grab Word, Excel, PowerPoint, Outlook, Access, and Publisher 2016 from the Windows Store; however, a search for OneNote still only shows the UWP app.
As it turns out, OneNote 2016 has been there all along, but as we were told at Microsoft's Build 2017 developer conference, it's just not obvious. Moving forward, the company certainly wants you to use OneNote for Windows 10, but in a rare, sensible move, is allowing users to use the desktop app to bridge the gap, understanding that there may be some obscure feature missing from the UWP app that's important to you.
You can download the app from the Windows Store here, but you'll need to be eligible for the Office 365 preview. In other words, if you can't already download, Word, Excel, and the rest of the pack, you won't be able to get OneNote, at least for now. You can learn more about OneNote in the Windows Store here.