The reason behind this is a security feature added in Windows 10. Technically it was present in Windows 8 too but only affected the metro apps in it. As the application executed in the Built-in account are automatically given elevated rights, the apps are blocked for use to prevent them from harming the operating system. As the Microsoft Edge was added in Window’s 10 as an app, it is now affected in Windows 10 too by this feature.
The message you see can be misguiding because it is untrue. You cannot run Edge in that account by default but it is possible if you are willing to make a few changes in your security options. Below are the methods given that you have to follow this one time only to run Microsoft Edge on a Built-in Administrator. There are 2 ways depending on the Version of Windows 10 you are running. To check which version of Windows 10 you are using, Press and Hold the Windows key and Press R. In the run dialog box, Type winver and Press Enter.
A system window will open. In it, next to Edition, if it is Windows 10 Home, then follow the method below. If it is anything else, then scroll down for the method for other editions.
For Windows 10 Home
What we will do is adjust the security settings in a way that allows us to sue Microsoft Edge through the Windows Registry.
Press and Hold the Windows key and Press R to open the Run dialog box. In it type regedit and Press Enter.
Registry Editor Window will open. In the left pane, Double Click on HKEY_LOCAL_MACHINE to expand it. Underneath it, locate SOFTWARE and Double Click it similarly expand it.
Similarly, navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System.
With System selected and highlighted in the left pane, you will see a key named FilterAdministratorToken in the right pane. If not, Right Click on the white background in the right pane. From the pop menu Click New > DWORD (32 Bit) Value and Name it FilterAdministratorToken.
Now Double Click on FilterAdministratorToken to modify it.
Under Value Data, Type 1 and Click OK.
Now in the left pane, Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System\UIPI\.
With UIPI selected and highlighted in the left pane, Double Click on Default in the right pane to modify it.
Under Value Data type 0x00000001(1) and Click OK.
Now Close the Registry Editor Window.
Now Press the Windows key to bring up the Search (Start) menu. Type UAC.
Click on Change User Account Control Settings in the search results.
In the Change User Account Control Settings window, Move the Slider on the left to the Second level from the top.
Restart your system and Microsoft Edge should be opening fine now.
For Other Windows 10 Editions
In this method the above done changes will be made in the Local Security Policy instead of Windows registry. Local Security Policy is unavailable in Windows 10 Home so the Registry method was used above.
To open Local Security Policy, Press and Hold the Windows key and Press R.
In the run dialog box, Type secpol.msc and Press Enter. Local Security Policy window will open.
In it, on the left pane, Navigate to Security Settings > Local Policies >Security Options.
With Security Options selected on the left pane, Locate User Account Control Admin Approval Mode for the Built-in Administrator account on the right pane. Double Click it to open its properties.
Select Enabled in the Local Security Setting tab and Click Ok.
Now Restart your computer and check of Microsoft Edge opens.
If not, then Follow the above method for Windows 10 Home edition. This combo has also worked for a few users who were still unable to open Microsoft Edge.