A family of Microsoft word processing software products for creating web, email, and print documents.
Thanks for the screenshots.
The 0x0 error is a known Microsoft Office for Mac activation issue, and it also affects Office 2021. Your current version, 16.78.3, is below the minimum Office version 16.83 required to resolve this.
You do not need to purchase Microsoft 365 or upgrade to Office 2024. You just need to update your existing Office 2021 installation. Office 2021 can still receive the current Office for Mac updates.
Please close all Office apps, then open Finder > Applications > Microsoft AutoUpdate. If you do not see it there, check:
/Library/Application Support/Microsoft/MAU2.0/
Open Microsoft AutoUpdate and choose Update or Update All for Word, Excel, and the other Office apps.
Microsoft also has a specific support article for the 0x0 error here: https://support.microsoft.com/en-us/support/known-issues/unknown-error-0x0-license-not-found-error-microsoft365-macos
Hold off on removing the license files for now, since Microsoft lists updating Office as the fix for this particular error.
If Microsoft AutoUpdate only gives you an Upgrade option and no Update option, can you share a screenshot of that window? That will help determine the next step.
Thanks!