Spurious Outlook Email Account needs deleting

That address is not a separate account. It is an alias on the same Microsoft account, so it shares the same mailbox, contacts and storage as your other addresses.

I would remove it from your alias settings, not from Outlook. Click Manage in that Email account screen, sign in, then choose Remove next to ******@outlook.com. If it is your primary alias, set ******@outlook.com as primary first, then remove it. Microsoft explains aliases and removal here: https://support.microsoft.com/en-us/accounts-billing/manage/change-the-email-address-or-phone-number-for-your-microsoft-account

Removing a Microsoft domain alias deletes it permanently, so check first that ******@outlook.com is listed there and is the address you want to keep.