An official YouTube app for Windows 10 appears to have shown up in the Microsoft Store.
Uncovered by Alumia, the app does not appear to be publicly available yet.
The app is a UWP app and does not appear to be a wayward version of the Xbox app, and according to ALumia is not a Progressive Web App.
However, at only a few tens of megabytes, it still seems likely the app will merely be a host for the YouTube website.
The app is not available when you search the Store yet, and it may still be a private app being worked on, and far from release.
After significant hostility around YouTube between Microsoft and Google some years ago, where Google refused to make a YouTube app for Windows Phone, and also refused to let Microsoft build one, and even at one point stopped YouTube from working on the Edge Mobile browser, it seems reasonable to ask why the app would come to the store now.
Things are however of course very different now between Microsoft and Google, with the companies cooperating on the Chromium browser, and Microsoft recently shipping an Android phone with the Google Search bar.