What is in the "Enter a URL for this link" field must be a valid URL. Do you know of a format for URL that includes CC? I do not.
I just checked: you cannot use multiple addresses in any safe way with a mailto: URL. Some clients might work, but failure is likely. The solution is to use a server script such as ASP, CGI, PHP .
Simply study the mailto syntax and you'll find out how to do it. See: https://www.labnol.org/internet/email/learn-mailto-syntax/6748/
Also, you said there isn't a way to email multiple people, but when I hit my submit button, it opens up an email in Outlook which allows me to send to multiple people:
Lastly, the article you linked says you can use the mailto function to populate a CC field, so I'm wondering why you say you can't?
Where did I say that?