Thanks for the reply. Referring to fullscreen button that appears from shortcode. (fullscreen=true) when using the alternative pdf loading. For example see here: https://sedgewick.io/talks/#21st-century-model
OSX 10.15.7
Browser Chrome, Safari, Firefox
For context, the reason we enabled alternative pdf loading was that we were getting errors on the entire page when loading mobile pages with several pdfs on same page, and alternative pdf loading helped with this problem.