Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi PolarBear,
Thanks for posting in the community.
According to your description, please try to install an older version of Office, like 16.29 or older in Release history for Office for Mac.
Also, based on my search, some members mentioned it was not available to activate Office in the operating system that is older than 10.14. If so, since the latest version of Microsoft 365 requires one of the three most recent versions of macOS, I would like to suggest you upgrade your macOS version.
If you have any updates, please feel free and come back to share with us.
Regards,
George