Internet Explorer mode currently available in Microsoft Edge dev and Canary builds is for Enterprises only, not for end-users as Microsoft confirmed to us that menu entry in Tools menu to show page in Internet Explorer is there before for internal debugging purposes and said they removed it after releasing IE mode to businesses. FYI, this option no longer appears in Edge Preview builds if you set “Enable IE Integration” flag to “IE mode”.

Microsoft announced IE mode at Build 2019 to offer a single browser that opens both modern websites and legacy apps, while Edge-based Chromium uses Blink engine, the Edge will open legacy sites in enterprise site list configured by IT admin in IE doc mode, this requires Internet Explorer 11 to present on the system to work.
During the Testing phase, IE mode worked in Windows 10 insider builds, later when it reached Canary and Dev builds, it has worked for us partially in Canary and fully in Dev build, but once Microsoft announced the next version of Edge with features such as IE mode is available for enterprise evaluation, the “Show this page using Internet Explorer’ option in More Tools menu stopped appearing and it disappeared.
@SeanOnTwt should be able to help.
— Colleen Williams (@CollWilliams) July 24, 2019
When we contacted Microsoft Edge team about this on twitter, we got the reply from Edge’s PM Syan Lyndersay we’re expecting: “the menu entry is there for Internal debugging purposes”
Lyndersay said they’ve removed the option (“Show this Page using Internet Explorer” ) after the IE mode was formally launched and highlights “IE mode is a enterprise-only feature. Only the admin controls whether a site ends up in IE mode or not”.
That menu entry was always intended only for internal debugging purposes, and we’ve removed it now that IE mode is formally released. IE mode is a enterprise-only feature. Only the admin controls whether a site ends up in IE mode or not (this is key to the security model).
— Sean Lyndersay (@SeanOnTwt) July 24, 2019
Expect the IE mode flag to vanish soon from new Edge preview builds. What do you say about this? Do you want IE mode?