Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hello, Muhammad Hafeez1.
Welcome to Microsoft community.
I understand your doubts, you seem to want to activate Office 2021 without an internet connection.
However, due to the reason below:
When a device loses Internet access, you can continue to use Office without an Internet connection for up to 180 days. However, when 15 days are left, you'll receive an in-client notification to connect to the Internet to verify your license. So, then you still need to connect your device to the Internet and enable it for an additional 180 days.
For these reasons above, you can't activate Office 2021 without an internet connection.
For more information, you can refer to the following support articles:
-<Overview of extended offline access for Microsoft 365 Apps for enterprise - Microsoft 365 Apps | Microsoft Learn>
Best Regards,
Hannah.Z- MSFT |Microsoft Community Support Specialist