Microsoft Edge Reading Mode
Thank you for posting your query on Microsoft Community. I will certainly help you with this.
Reading view is more streamlined clean and simple layout, book-like reading experience of webpages, without the distraction of unrelated or other secondary content on the page. This will bring whatever you're reading front-and-center. You can even change the reading view style and font size to suit your mood.
If the Reading view icon is grayed out, then that webpage does not support turning on reading view for it. I suggest you to try using it on other website and check if it helps. The alternate option to toggle between reading mode is by pressing Ctrl + Shift +R keys.
Hope this information helps. Post back with updated issue details for further help.