If you have an online URL ending with.xlsx, Google and Microsoft provide online viewers.

Microsoft should work better with their proprietary XLSX components: https://view.officeapps.live.com/op/view.aspx?src=https://www.sqa.org.uk/sqa/files_ccc/progression-2023-tables.xlsx

Google's more basic viewer: https://docs.google.com/gview?url=https://www.sqa.org.uk/sqa/files_ccc/progression-2023-tables.xlsx

I have done some tests with mime-type of word documents .docx

File saved with King Soft: ks.docx
File saved with LibreOffice: xj.docx
File saved with MS Word: word1.docx

word1.docx:application/vnd.openxmlformats-officedocument.wordprocessingml.document; charset=binary
ks.docx:application/zip; charset=binary
xj.docx:application/zip; charset=binary

PHP script to get these results:

<?php
$finfo = finfo_open(FILEINFO_MIME);
echo 'word1.docx: ' . finfo_file($finfo, 'word1.docx') . '<br/>';
echo 'ks.docx: ' . finfo_file($finfo, 'ks.docx') . '<br/>';
echo 'xj.docx: ' . finfo_file($finfo, 'xj.docx');

As you can see it's mime-type that is wrong from other non-ms-word programs.