
The flag can't launch Edge into IE mode directly and AFAIK there's no such command. I recommend you try out another IE mode entrance by configuring the following group policies. So you can automatically open sites that you want to load in IE mode.
- Configure Internet Explorer integration
- Use the Enterprise Mode IE website list (Internet Explorer)
or Configure the Enterprise Mode Site List (Microsoft Edge, version 78 or later)
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Regards,
Yu Zhou