WordPress default theme CSS version problem and not loading

you can pass time() function in version parameter. so you dont have to change version to update a css code.

function add_dynamic_version_css_scripts() {
    wp_enqueue_style( 'dynamic-style', get_template_directory_uri() . '/css/custom-style.css','style-css', time() );
}
add_action( 'wp_enqueue_scripts', 'add_dynamic_version_css_scripts' );

let me know if this works for you.