I very much like the UWP version and prefer it over the desktop version

It's a shame they are killing it

This goes to show that Microsoft is completely pulling the plug on first class touch support for their products to support surface devices. Since Panos Panay left Microsoft, surface devices have been losing what makes them special.

About time. Can they do it retroactively, or does this just mean no more security updates?

for Windows 10

Thank God. I was afraid because I use OneNote for work.

Microsoft will end OneNote support, and the app will no longer receive new features and security updates. As such, users are strongly recommended to migrate to OneNote for Windows desktop app

Is this the UWP version, or just the "windows 10" version?

The non-x86 version is absolutely awful and deserves to die - the desktop version is fine, and not a bad tool for organizing notes and taking meeting notes when your company uses Microsofts tool house (i.e. you have no choice).