How to install Microsoft on Mac with older operating system

Install Microsoft 365 for Mac version 16.66/16.66.1, rather than the current installer, because this older build is compatible with macOS Catalina 10.15.7.

Install the Catalina-compatible build

1. Close all Microsoft Office applications.
2. If the incompatible current release is partly installed:
   • Open Finder → Applications.
   • Control-click each Office application and select Move to Trash.
3. Download the Microsoft-hosted Office 16.66.1 full installer: Microsoft Office 16.66.1 installer This installer was the accepted resolution for the same Catalina 10.15.7 installation problem.^1^
4. Open Finder → Downloads, double-click the downloaded .pkg, and complete the installation.
5. Open Word or Excel and sign in with the Microsoft account associated with the active Microsoft 365 subscription. A valid licensed account is required to create and edit files.^2^
6. Confirm the installed version from Word → About Microsoft Word. It should show version 16.66.x.

Microsoft’s official release history lists the October 2022 Office 16.66 full installer and the 16.66.1 application updates.^3^

Important limitation

Catalina is outside the currently supported macOS range. Office can continue to work on an unsupported macOS version, but it no longer receives feature or security updates.^4^

If the Mac can be upgraded, that is the safer long-term option. If it cannot, use the older desktop build with that limitation in mind, or use Microsoft 365 on the web for a currently maintained experience.^5^

If installation or activation fails

• If the .pkg does not open, wait until the download finishes, move it from Downloads to the desktop, and open it there.
• If Office installs but shows the wrong license, remove the existing Office license files and reactivate using the account tied to the Microsoft 365 subscription.^2^
• If Microsoft AutoUpdate offers a release requiring a newer macOS version, do not install that release while remaining on Catalina.

References

1. how to install 365 on my Mac OS catalina 10.15.7 - Microsoft Q&A
2. [Activation](https://support.microsoft.com/microsoft-365-activation-licensing/what-to-try-if-you-can-t-install-or-activate-office-for-mac)
3. Update history for Office for Mac
4. Upgrade macOS to continue receiving Microsoft 365 and Office for Mac updates | Microsoft Support
5. Update Microsoft 365 or Office on your macOS or iOS device | Microsoft Support