Thanks Prisca for feedback. It’s always good to use those sort of tool to optimize your site. Is there any child theme is provided with @import ? If yes then let us know we correct that.
Furthermore, what you did is find do work but it’s always good to enqueue the script rather than using <link href tag on WordPress .
See the example of how it is done in Pure & Simple child theme.
function puresimple_child_enqueue_scripts_styles() {
wp_enqueue_style( 'parent-theme-css', get_template_directory_uri() . '/style.css' );
}