Edge Chromium Preview as default browser

danholme   You aren't missing anything.  W10 in S mode locks you into Edge.

Unless you hear something different from one of the Microsoft employees that participate in this forum, I think you will just have to put up with it.

From https://support.microsoft.com/en-us/help/4020089/windows-10-in-s-mode-faq :  "Can I set Google Chrome or Firefox as my default web browser when I'm using Windows 10 in S mode?  No. When you're using Windows 10 in S mode, Microsoft Edge is always the default web browser, and Bing is the default search engine. But you can access other browsers and search engines while in S mode. You can download any browser available in the Microsoft Store in Windows, and you can navigate to any other search engine website."

I suspect that W10 S treats Edge Chromium is a "foreign" browser, that is, not-Edge, and accordingly Edge Chromium is treated no differently than Firefox or Chrome.