I found the solution, the email address in question was still signed in on Microsoft Word.
Once I signed out of the account on Word, the email address was not automatically found in Outlook.
I am using Outlook 2021 on Windows 10 and 11. I have the exact same issue on both systems of Outlook automatically searching and finding an old email account including the password.
I have deleted and created a new profile multiple times and the old account still shows up.
I have checked...