Follow this notebook as example, is it possible to inject a javascript code into the browser console for all cells to be visible?
On the notebook page, go to the Chrome Console tab (F12) and paste the code below. Invisible cells have the class "sc-jSMfEi imrMBR". The code identifies each one and clicks on them to make them visible.
list_hiddencode = document.getElementsByClassName("sc-jSMfEi imrMBR");
for (var i =0; i < list_hiddencode.length; i++){
list_hiddencode[i].click();
}