On .Net Core 3.0 Preview 3, Asp.NET Core Identity Template, register a user with username
bernhard@günter.com
Expected
Validation responds that this is not an allowed character for a username since the default is
public string AllowedUserNameCharacters { get; set; } = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._@+";
Result
bernhard@xn--gnter-kva.com is stored in the db as username and email and displayed in the UI!

That is pretty unexpected for an old framework and a handicap in the current implementation.
Probably this has been encountered in the past??