In functions.php

// set these styles as PRELOAD
function add_rel_preload($html, $handle, $href, $media) {
    if (is_admin()) {return $html;}

	$html = '<!--'.$handle.'-->'.$html;
	if( $handle=='infocus-style' || $handle=='wp-block-library' ){
		$html ='<link rel="preload" href="'.$href.'" as="style" onload="this.onload=null;this.rel=\'stylesheet\'" id="'.$handle.'" media="all"><noscript><link rel="stylesheet" href="'.$href.'"></noscript>';
	}
    return $html;
}
add_filter( 'style_loader_tag', 'add_rel_preload', 10, 4 );