Sorry, yup, both settings work together and are required.
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For all that were looking at this... I think I found the issue. It looks like that setting is not supported whenever the browser is "managed by your organization" - which means, if you have ANY group...

Yes, I know that... that is precisely why we REALLY need to have the "IE Mode" option enabled in Edge!! Older SharePoint forms don't work properly in Edge (the rich text editor). It does when loaded...

I have the same problem as well. The setting is missing on my (all) work computer's Stable Channel version, but it's there in Canary Channel. It's also there on my home computer's Stable Channel...