
Hi @enami,
AFAIK, Office Viewer on Microsoft Edge is the only OFFICIAL solution to allow users to view Office files in the browser, if your resources are stored on your organization's website. Since it requires authentication, then Office Viewer is not an option for you which requires files to be "public".
Of course, there're still 3rd-party solutions which may meet your needs. You can take a look at them.
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Best Regards,
Shijie Li