You cannot simply "extend" the preview. You must remove the preview licensing and convert the installation to a licensed, retail, or volume-licensed version of Office 2021.
| | Avoid this | |--------------|----------------| | Office LTSC 2021 Volume License (perpetual, no expiration) | Office LTSC 2021 Preview | | Office 2021 Retail (Home & Business / Professional) | Time‑limited trials from unofficial sources | | Microsoft 365 subscription (continuous updates) | “Evaluation” copies for production use | You cannot simply "extend" the preview
A full license was purchased, but the local machine is still reading cached beta licensing certificates. You cannot simply "extend" the preview