Problem Turning On Mail | Using it for the First Time and I want to set up my @icloud.com email - which I haven't been able to

Hi!

I've recently wanted to switch to using iCloud Mail, but, for some reason I am not able to do that. I don't have an @icloud.com account, so I tried creating one by switching on the iCloud Mail. However, once I enter my desired username, it shows me an error. I've tried signing out and signing back in, and it still doesn't work - I've done this on my iPhone and my MacBook Pro. Is there any way I can get some help in being able to create my account otherwise?

[Image Edited by Moderator to Remove Personal Information]