As indicated on https://docs.microsoft.com/en-us/deployedge/edge-ie-mode IE mode does not support IE11 or Microsoft Edge F12 developer tools.
We are actually planning to migrate 30'000 Windows 7 desktops to Win10/Office365-Cloud Services. Actually we have a dual browser strategy with Chrome and IE11. There are still some business critical applications depending on IE11. A crucial pre-condition for migration to Win10/Office365 is the ability to decouple browser adoption dependencies from Win7 -> Win10/Office365 rollout.
The strategical move to Chromium Edge with IE-Mode, available on both platforms is already a big help for this. Great.
Now, our production support is used to have the 'developer tools' feature available for debugging in with IE11. It would be a crucial pre-condition to have these debugging capabilities available on Edge-Chromium IE-Mode as well.
What are the obstacles for providing F12 Developer/Debugging features in IE-Mode?
Might be, MS was just not aware of this use case at the time of deciding this.