When you cannot sign in to activate office 2021, the users will receive a message:

1.We are unable to connect right now. Please check your network and try again later.

2. Sorry, we can’t connect to your account. Please try again later.

This article highlights on how to troubleshoot the activation issues in Microsoft Office 2021. Consequently, the activation fails and you receive these error messages. To restore all features of Office 2021, fix the problem that is causing activation to fail.

https://officesupportcontact.com/cannot-sign-in-to-activate-office-2021/