Apple Music profile name - Won't let me type any characters before the @

I want to set a profile name for my Apple Music so that I can share my music. The programming won't let me type in anything in front of the @ sign. Everything I type gets put in after the @ sign, which apparently is where icloud.com should go.

1 - How do I fix this?

2 - After this is fixed, can I type in a new password-like name, or does it have to be a previously recognized Apple name, & if so, which one?

I'm running Ventura 13.6.3 on my 2017 64 GB iMac (or iMac Pro? Don't know how to tell which it is) & Apple Music 1.3.6.14.

Thank you