In the target field, add the string --enable-features=ExtensionsToolbarMenu after "C:\Program Files (x86)\Microsoft\Edge Dev\Application\msedge.exe" as shown below.

The about:flags settings page in Microsoft Edge browser lets users enable more features. Learn how to enable & use these features.

When Microsoft's Edge browser first rolled out, one complaint was the lack of a full-screen view. That issue has been addressed, with three different methods.