You need to open the document like this:

window.open('https://view.officeapps.live.com/op/view.aspx?src=' + publicUrl);

This will open files in a new window.

If you want to display the document in an iframe, use:

https://view.officeapps.live.com/op/embed.aspx?src= + publicUrl

Also make sure that your Nginx configuration allows external requests by enabling the appropriate CORS settings. Otherwise, Office Online will not be able to download the file from your server.