Computer Configuration > Administrative Templates > Microsoft Edge
Both
HKLM\Software\Policies\Microsoft\Edge
This policy controls whether to always keep the active Microsoft Edge window with an Internet Explorer mode tab in the foreground. If you enable this policy, the active Microsoft Edge window with an Internet Explorer mode tab will always be in the foreground. If you disable or don't configure this policy, the active Microsoft Edge window with an Internet Explorer mode tab will not be kept in the foreground. To learn more about Internet Explorer mode, see https://go.microsoft.com/fwlink/?linkid=2094210