I have the same problem. I can't authentificate in Win11 with Edge as standard browser.
Edge opens, I can enter the PIN shown on my iPhoone, but then nothing happens.
When I define Firefox a standard webbrowser, firefox asks to open an URL and after I agreed, Enpass syncs via iCloud.
Due the authorisation works with Firefox, I asume it is a problem with Edge and not a problem of iCloud, DNS or firewall/proxy/...