It seems that Microsoft has quietly backported the block, introduced a month ago in a Dev build of Windows 11, on tools like EdgeDeflector and browsers from being the true default browser in Windows 10, with the change being implemented in Windows 11 too. Starting from KB5008212, which was installed on all supported versions of Windows 10 yesterday with Patch Tuesday, it is no longer possible to select EdgeDeflector as the default MICROSOFT-EDGE protocol.
The change was also ported to the current version of Windows 11 with yesterday's Patch Tuesday with the installation of KB5008215 rendering it impossible to choose anything but Microsoft's Edge browser.
Upon installing the KB5008212 update in Windows 10, the EdgeDeflector choice is removed, and the first time you open a link from the OS level - which you can invoke by right clicking on Start and choosing Run, and then typing microsoft-edge:https://www.neowin.net -, you will be prompted to select a default browser and you can only select Microsoft's Edge browser or "Search for an app in the store".
Fortunately, there's a workaround against these anti-competitive ... and desperate measures; first discovered by gHacks, the open source tool MSEdgeRedirect uses a completely different method. Instead of relying on the (now blocked) protocol handler, it "filters and passes the command line arguments of Microsoft Edge processes into your default browser ". So, although it no longer relies on the protocol, the tradeoff is that it needs to be running in the background to work its magic. But you have to ask yourself, how badly do you want to "deflect" Microsoft's Edge browser?
All the app does is redirect links that are designed to open in Microsoft Edge. In a future version, it will also be possible to set the default search engine, since without tools like EdgeDeflector and Mozilla's Firefox, search terms from places like the Start menu opens Microsoft's Bing instead of your chosen default search provider.
As of writing, the latest version is 0.4.1.0 and upon launching the installer, Microsoft's SmartScreen pops up and blocks the app from running, but you can choose Run anyway to install it. gHacks notes that browsers and security applications may display warnings about the program: it is new and designed with AutoIt, that's the reason why it may be flagged.
Ultimately, it's up to you if you want to take back control.