Primary Email Address from Gmail to Icloud

Hello, When I am trying to change the icloud address as the primary address I am having an error which is I cannot add it during this time. And upon trying to create a new apple account and they are asking to input an email address it is not allowing me to create using icloud.com email. By the way this is for my partner’s account.

I also have a question regarding the No location found in Find my iphone. Since the gmail address is the primary address is that the reason why I cannot locate the phone?

Thank you for the assistance.