Link to external URL

Without http:// in front, your code won’t work. You will need to add that infront. You can make use of parse_url to add http:// to urls that does not have that.

To make this protocol agnostic, you can simply use //

You can try something like this

$urlStr="www.google.com";
$parsed = parse_url($urlStr);
if ( empty( $parsed['scheme'] ) ) {
    $urlStr="//" . ltrim( $urlStr, "https://wordpress.stackexchange.com/" );
}
echo '<a href="' . $urlStr . '">External</a>';