Why doesn't outlook.com have a plus sign in the Edge address bar like other Chromium browsers do?

DaveLPG outlook is not yet a PWA. I'm not sure if they have a timeline yet for becoming one or not, unfortunately. However, you get basically the same experience when you "install site as an app" as you do from a PWA, the differences are subtle.

In order to get the "Plus" sign in the omnibox for install, three things must be true:

1. the site is served over HTTPS

2. the site has a manifest json file at the root of the domain

3. the site has service workers

You can always go to webhint.io and run a scan on any url to get a "PWA" score. 

All that said, we expect that end users will really not be able to tell much difference between a "real" PWA and a site that is installed. Primarily, the differences will come from what would be contained in the manifest, as well as potential offline capabilities.

-John