WP Fastest Cache -> Render Blocking Js -> Exclude Js Sources

Question

You could use the script_loader_tag filter hook to accomplish this. This hook passes in the tag HTML that you can search on, then add in your data attribute.

/**
 * Modify script tags as they're loaded
 *
 * @param String $tag_html
 *
 * @return String $tag_html
 */
function wpse379555_script_tag( $tag_html ) {

    if( false === strpos( $tag_html, 'wpfastestcache' ) ) {
        return $tag_html;
    }

    return str_replace( ' src="https://wordpress.stackexchange.com/questions/379555/," data-wpfc-render="false" src=", $tag_html );
}
add_filter( "script_loader_tag"https://wordpress.stackexchange.com/questions/379555/,"wpse379555_script_tag' );