IE Mode is a feature in Microsoft Edge that allows access to legacy sites that only support Internet Explorer 11. In the case of ETO this means that it can be used to access legacy features that otherwise were restricted to use with Internet Explorer.
Note that this feature requires Internet Explorer's settings be configured to access ETO to work properly. Details on configuring those settings can be found here.
More details on the feature and its use case can be found in Microsoft's documentation site. (https://docs.microsoft.com/en-us/deployedge/edge-ie-mode)
Note that this feature requires Windows to work and is not supported for the MacOS version of Microsoft Edge.
How to Enable
1. Open Microsoft Edge
2. Open the settings by clicking the elipses icon in the top right, followed by clicking the settings selection
3. Click on the Default Browser section the Setting's sidebar
4. Under the "Internet Explorer Compatibility" section, turn on the "Allow sites to be reloaded in Internet Explorer mode” toggle switch.
5. Click the Restart button
How to Use
Once these steps have been completed, you will then need to enable IE mode when visiting legacy pages. This is done by clicking the IE Mode Icon in the top right corner of the browser. Not all pages will be able to switch to IE mode.
If you do not see the IE Mode Icon at the top of Edge, you should find it in the menu under the ... icon as seen below.