very common.

just set another alias and disable your main alias. otherwise you will still get relentless sign in attempt.

No. It means login using an alternate email, for example, ur email is abc@outlook.com, u create another email abcd@outlook.com as an alias, and set this as primary email. Then in the future, every time when u login, u can only use abcd@outlook.com to login, if u try to use ur actual email, u will get email not exist. However, ur actual email is still active, just that when someone use ur email want to login, it will say email doesn't exist.