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This appears to be only for Edge?

Edge (Chromium), so shouldn't be a problem in practice given every website has to be Chromium-compatible anyway.

I'm guessing the real objection is needing to run Windows to use this. Unless Edge runs on other OSes?

The new version of Microsoft Edge can be downloaded for macOS and Windows, but I'm not sure about Linux.

Preview coming later this month.

You could have spent the 2 minutes to google this https://www.microsoft.com/en-us/edge

(it works on macOS)

And Linux Beta is supposed to arrive this month.