Unable to sign into Microsoft Office 2021

Hi GreenGene,

There are some possible solutions that you can try to fix this issue:
- Reboot your device and try signing in again.
- Run the following commands in PowerShell as an administrator to repair WAM. 

$manifestPath = (Get-ChildItem $env:windir\WinSxS -Filter Microsoft.Identity.Authentication.WamRuntime.dll -Recurse). FullName | Select-Object -First 1
$manifestPath = $manifestPath -replace "Microsoft.Identity.Authentication.WamRuntime.dll", "Microsoft.Identity.Authentication.WamRuntime.manifest"
DISM /Online /Cleanup-Image /RestoreHealth /Source:$manifestPath

- Update your Office to the latest version. Open any Office application, click File > Office Account > Update Options > Update Now.
- Remove and re-add your work account from Windows Settings > Accounts > Access work or school. Find your Microsoft 365 work account and click Disconnect, then click Connect and sign in with your credentials.
- Run the Microsoft Support and Recovery Assistant: This is a tool that can diagnose and automatically fix several common Office sign-in issues.
- Reinstall Office: If none of the above steps work, you might need to uninstall and then reinstall Office.