How do I delete my @iCloud.com email if it's no longer my Apple ID?

I already tried going into My Account page to Remove/Delete it and also via my updated iPhone but it doesn't give me the option. It only gives me the option to delete my current Apple ID which is a third-party email. The @iCloud.com email was my first to be associated with my Apple ID I think. And it was the same as my original gmail only instead of @gmail.com it was @iCloud.com That Gmail is now deleted or forgotten so I wanna remove all connections to it.

Especially when Google doesn't respect privacy but Apple does. In fact, Google and Samsung stole Apple's touchscreen technology but that's an issue for another time.

Also, would anyone with access to my Gmail be able to sign-in to my Apple ID since the @iCloud.com is the same as my Gmail only it's @iCloud.com? I enabled two-factor authentication recently. I have just changed my iCloud password, had all iCloud devices sign-out, then I logged back in. Because I guess somebody was hacking/hacked my account or had access to it, because Apple was asking me to create a new password, verify myself,...

I just got a new iPhone and I still have my old one. I had to delete my old one which has 10.3.3 btw from list of trusted devices when I thought I had already done so both remotely and then by wiping it via recovery mode while plugged-into my macbook.