I don't see how this could be related to writing part, because the error is raised at the time when you try to load the file you want to append to, before anything else.
Even in the unlikely case the user on SO is right that [in general] pandas overwriting existing file with a empty one may produce an error somehow, this is not your case - you load a xlsx workbook, append a sheet with data and try overwrite the file you read with the updated file. You don't overwrite with empty file.
Did you try with different file? Is there something different (apart from updated python/packages) compared to when it was working?
Even in the unlikely case the user on SO is right that [in general] pandas overwriting existing file with a empty one may produce an error somehow, this is not your case - you load a xlsx workbook, append a sheet with data and try overwrite the file you read with the updated file. You don't overwrite with empty file.
Did you try with different file? Is there something different (apart from updated python/packages) compared to when it was working?
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How to Ask Questions The Smart Way: link and another link
Create MCV example
Debug small programs