Current status
While Google can quickly implement new browser features, other companies such as Microsoft are much slower. AVIF was created as part of developing AV1, which was developed by the Alliance for Open Media. Since all the major browser manufacturers are part of this alliance and everyone is interested in displacing a new and modern format, you expect Microsoft Edge to support AVIF files soon. At the time of writing, Edge does not yet support AVIF images; it refuses to render or otherwise open AVIF images.
Your Edge version
If you are looking for a way to test the functionality and capabilities of AV1 on Microsoft Edge, you should download the latest version of the browser. The new Microsoft Edge is based on Chromium and was first released in early 2020. It is compatible with all versions of Windows and macOS for whatever reason. Microsoft claims it is the only browser you will ever need, but well, who wouldn't say that about their own browser. You can quickly determine if you own a Chromium version of Edge by looking at the browser icon. The new version of Edge has a more minimalist and gradient style, while the old one looks like a Van Gogh.
AV1 Plugin
The AV1 Extension add-on is available from the Microsoft Store. It provides support for AV1 videos on Windows 10 devices and Edge. It also allows viewing AVIF images, including thumbnails, and editing in Paint.