Microsoft is testing a built-in Office Viewer for Microsoft Office documents in the latest Edge Insider builds.
The feature, which is present for some in Edge Dev 92.0.873.1 and above, dispenses with the Office Viewer extension for Edge and lets you preview Office files in Edge in much the same way you can preview PDFs.
For those who have it enabled, you can activate it in the Download section of Edge Settings.
Unlike the Office Viewer extension, however, the feature only works for Office files on the web and not OneDrive.
The feature appears to be part of a controlled roll-out and is currently not available to all.