This only happens when trying to view or download wp-config.php of Wordpress from cpanel
In addition to this yesterday I got an error when analyzing the website with Pagespeed, something like: error when loading document. I reinstalled Wordpress and from then on is loading fine in Pagespeeed, but all of this is sort of suspicious. Additional info of the screenshot: Cloudflare Ray ID: 784621f2ee5fd76a
Edit: minor correction: when attemptimg to download the file nothing happens.
I’d rather say it’s security measurement added to the file which disables feature of editing wp-config file through the WordPress admin dashboard for protection from some strange behaviour of the plugin with some vulnerability, otherwise for protection and disallowing of modification of it which could be done by one of the user account(s) whom shouldn’t have access to it at first sight.
Otherwise, kindly I’d suggest you to take a look at the below posts: