This is a bit of a dupe of https://news.ycombinator.com/item?id=29191244 - but article confirms (via Microsoft's release notes) that they consider it a bug that applications which are NOT Edge were able to set this.

> We fixed an issue where OS functionality could be improperly redirected when microsoft-edge: links are invoked.

There are also some paid options which show - when you try to change the handler for `microsoft-edge:` (you can't pick an app; but you can pick Microsoft Store). `Search Bar Connector` for 1.69 and `Search Deflector` for $1.69

Guessing these are broke too. If it really is a "bug", why did Microsoft approve those applications?