Sending, receiving, and organizing email in Outlook.com
That weird address is because you have a non-Microsoft address set as primary on your Microsoft account. Your address is used only to sign into Microsoft services and the weird address is a placeholder for an outlook.com address.
Set an outlook.com alias as primary at https://account.microsoft.com/profile/ and it will go away.
Microsoft has more information in this article:
Outlook.com email account appears as "outlook_[long series of letters and numbers]@outlook.com" in Outlook for Windows
https://support.microsoft.com/office/90ed7938-7f21-4cb5-a69d-a3b79ea4eafd
Mail from non-Microsoft address will not sync yo outlook.com on the web.
-- Diane