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 );
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.
disables the ability to edit core WordPress files from either within the WordPress admin or via direct file access
disables the theme and plugin editor in the WordPress admin
prevents any non-admin user from directly editing theme or plugin files