Hi @Sekh, Sahammad ,
First, for the current Microsoft Edge, it uses the integrated Chromium engine for modern sites, and uses the Trident MSHTML engine from Internet Explorer 11 for legacy sites. So IE mode will always work if you install the Windows and Microsoft Edge browser correctly. You could refer to this document for more details.
Second, about the IE mode setting you mentioned. As described in the last paragraph of the document you provide, it depends on this InternetExplorerIntegrationTestingAllowed Edge group policy setting. Therefore, it has nothing to do with whether to install IE browser or not.
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Regards,
Yu Zhou