Even with third-party email address for Apple Id, I still can login to the same Apple Id with my @icloud.com email

Here is the explanation:

Some years ago I created my Apple Id with @outlook.com email. Than I enabled @icloud.com email. When I lost the access to my @outlook.com email, I was urgent to change my Apple Id and the only email that I had was @icloud.com. Soon I started to changing all my registrations with the new @icloud.com email (I found the email aliases later :( ). It was good, until I realized that if I cannot access my @icloud.com, I also cannot access my entire Apple Id, so I changed my Apple Id to third-party email address, and here is the problem: My @icloud email appears in Reachable at saction as alias to my Apple Id and I'm able to sign in to Apple Id with @icloud.com email. After Sign in my Apple Id is labeled as the third party email.

My concern is about possible leak of the @icloud email and attempt to be used for access to my Apple Id.

Yes this is impossible without the password and the Two-factor authentication, but it will be ways better if I can decide with which email I will be able to sign in.

For example: years ago I was able to turn off "sign in with" option for my Outlook.com alias.

I hope someone from Apple will read this and things to be changed.

Meanwhile is there any possible way to disable @icloud.com sign in possibility?

I cannot delete it from any website that this email was appeared.