Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Can you sign into your personal account via this link: https://account.live.com?
If so, go to Your Info > Sign in preference, Add an alias.
You have two options here:
Create new: this will allow you to use the native domain outlook.com to create a new alias.
Add existing: this will allow you to add a 3rd party email address, such as yahoo, gmail, as long as they are not already associated with another Microsoft account.
Once added, make this new alias your primary alias, then you can delete the other email as alias, and that email is free from this Microsoft account instantly.
Quite important, also head over to Security > Manage how I sign in. Update here too if necessary so you can continue to receive 2FA code.