In your wp-config.php file, you've added the following line of code. What does it do? define( 'DISALLOW_FILE_EDIT', true );
define( 'DISALLOW_FILE_EDIT', true );
disables the ability to edit core WordPress files from either within the WordPress admin or via direct file access
sets read-only permissions on all files in the WordPress install More WordPress Security: Disallow File Edit Setting In WordPress. Setting all files to read-only would make auto-updates impossible.
prevents any non-admin user from directly editing theme or plugin files
disables the theme and plugin editor in the WordPress admin