Default browser has to be something as lite as possible, probably Pale Moon. Because random apps use to call the browser any time they want and if the default browser is browser I use, it eats a lot of time and laptop battery trying to start my hundreds-tab monster.
Edge was great just after they switched to Chromium and lead the way on battery optimizations. And then every team started an everlasting "who can exhaust the patience of their users the fastest and get them to either give in to microsoft-everything or switch away from edge" contest.
That makes me wonder: What are the rules for something to be considered a browser? Does it need to provide certain functionality, or can I register anything as a browser and just have links open in an editor?
I tried exactly that. Turns out it can't be a .bat or .ps1 for understandable reasons, it has to be an executable. So, my "default browser" on this machine I'm on is now an .exe that prints $1. It works.
In Windows, default applications are registered either by URL scheme (so ftp, http, https, gopher...) or file extension (.txt, .html, .pdf, .mp4...). As far as I know there is no special registration for "browsers" specifically, you just register your application as a handler for whatever protocols and file formats you want.
So if you want to make your random executable be "a browser", my guess is you should register it as a handler for http, https, and .html, at least.
