Why do i need a new email account to sync my notes in iCloud? I'm trying to sync Notes from mac to iPhone. But when I turn on Notes in iCoud, it says that I require an iCloud email address. This is unexpected since my Gmail account is alreadyh linked with my iCloud account.

Why is an iCloud email address required to sync Notes?

(I'm able to sync Reminders with no problems.)
iOS Notes syncing works through the IMAP protocol, which in iCloud is integrated into the email service. Although Apple could technically choose to allow for notes syncing without explicitly requiring an email address, they have chosen to make it a part of the email, almost like Notes is its own email folder.

You should also be able to sync your Notes using your Gmail account since it is also based on the IMAP protocol: