Hi Hoang Pham4,
To rule out any potential impact from your existing Office 2021 license, I suggest clearing the license information using the following method to see if it resolves the issue.
First, press the Windows key + S, search for "cmd" in the search box, and right-click on "Command Prompt" in the search results to select "Run as administrator."
Enter cd C:\Program Files\Microsoft Office\Office16
Enter cscript ospp.vbs /dstatus (note the space after .vbs, use English input method to enter the command)
and then enter the following command to uninstall the last five digits of the key:
cscript ospp.vbs /unpkey:(last five digits of the key) [e.g., cscript ospp.vbs /unpkey:KHGM9].
Enter cscript ospp.vbs /dstatus again to verify if there are any other keys, and repeat the above steps if there are.
After completing the removal of residual Office information, reopen your Office. Feel free to share the result with me.
Jonathan Z