Perfect. That's super helpful. So you basically were using your old work email address as your personal Microsoft account's alias. This can be easily addressed.
Go to https://account.live.com
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, Don't delete the old email address yet.
Then go to Security > Manage how I sign in, here, make sure you update your contact information, add new one if needed, then delete the old work email address, only on this page.
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Then on your computer, Go to Settings > Accounts > Your info
Click on Sign in with local user instead. follow the steps and finish the rest.
(If you don't see the "sign in with a local account instead option, click on "Stop signing into Microsoft apps automatically" first, then relaunch this page. )
Restart the computer (Do Not skip)
Go to Settings > Accounts > Your info
Click on Sign in with Microsoft account instead. follow the steps and finish the rest. This time sign in using the new primary alias you used above.
Restart the computer (Do Not skip)
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Now you can go back to https://account.live.com > Your info > Sign in preference, you can delete the old work email from here.
This whole process will not affect your data, or your subscription. It is still concisdered the same Microsoft account, but we just swap out the alias/username used to sign into this Microsoft account.