Hi @Changshin Gwak ,
The only way for downloading the Office 2021 LTSC is using the Office Deployment Tool:
https://learn.microsoft.com/en-us/deployoffice/ltsc2021/deploy
You can use the ODT to download the Office LTSC 2021 installation files to local:
setup /download configuration.xml
https://learn.microsoft.com/en-us/deployoffice/ltsc2021/deploy#download-the-office-ltsc-2021-installation-files
This the way to install Office LTSC 2021 from local, hope the information is helpful. Please let us know if you would like further assistance.
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