How can I get Home Office and Student (2021) to work an a Mac after a minor system update

Yes. On a Mac, removing the Office license files and then reinstalling Office is a supported path, especially after an update when Office 2021 no longer opens or activates correctly.

Recommended order:

1. Remove the Office license files
   • Download and run the Microsoft license removal tool.
   • Open the .pkg file from Downloads.
   • If macOS shows an "unidentified developer" warning, hold Control and click the file, then choose Open.
   • Select Continue and complete the setup wizard.
   • When prompted, select Install to remove the licenses.
   • After it finishes, select Close.
2. Open an Office app and sign in again
   • Open Word, Excel, or another Office app.
   • Sign in with the Microsoft account associated with the Office Home & Student 2021 for Mac purchase.
   • Restart the Mac after activation.
3. If Office still will not open or activate, uninstall and reinstall the apps
   • Close Word, Excel, PowerPoint, and Outlook.
   • Open Finder > Applications.
   • Locate the Office apps, Control-click each one, and choose Move to Trash.
   • Reinstall Office from the installer for the version in use.
4. Important Mac App Store note
   • If the apps were installed from the Mac App Store, those versions require a Microsoft 365 subscription and do not support a one-time Office Home & Student license.
   • In that case, remove the App Store versions and reinstall Office directly from Microsoft.
5. If the issue started after a recent update and shows license errors such as "Unknown Error 0x0" or "License Not Found"
   • Make sure macOS is version 12 or higher.
   • Close all Office apps.
   • Open Finder > Applications > Microsoft AutoUpdate.
   • Select Update All or update the Office apps individually.
   • Then launch Office again and test.

Caution: before removing licenses, confirm the Microsoft account that owns the Office 2021 license so the correct account is used during reactivation.

• How to remove Office license files on a Mac
• Microsoft Office activation and the Mac App Store
• What to try if you can't install or activate Office for Mac
• Unknown Error 0x0 or License not found error in Microsoft 365 or Office running on macOS
• How do I upgrade Office?