I'd like to suggest Edge differ from Google Chrome in how light/dark mode is controlled. Although defaulting to the OS dark/light preference is fine, it'd be nice to have the option to detach Edge-Chromium from the OS preference, to specifically choose light or dark, like in Edge 18, at least. (Would it be too crazy to suggest it be per-site?...)
Furthermore, I understand there's spec to allow sites to use dark/light preference (https://drafts.csswg.org/mediaqueries-5/#descdef-media-prefers-color-scheme), which appears to be implemented as of Edge 76, making it possible to be "dark all the way down", but here too I wonder if locking to OS preference will be best for users' comfort. Even more than the browser UI itself, this is similar to zoom... what works for OS & user isn't necessarily what works for a specific site & user, because the site designer had a difference of opinion. It's good to have some choice about it, especially on sites you frequent.
I agree with the dark/light mode being separated from the OS settings, but personally, I think tieing it directly into website styles is a bit too much. I think that would be better left to extensions.