Remove query strings from static resources in WordPress. Source: https://perfmatters.io/docs/remove-query-strings-from-static-resources/

remove-query-strings-wordpress.php

/* Remove Query Strings
/***********************************************************************/
add_action('init', 'remove_query_strings');
function remove_query_strings() {
	if(!is_admin()) {
		add_filter('script_loader_src', 'remove_query_strings_split', 15);
		add_filter('style_loader_src', 'remove_query_strings_split', 15);
	}
}
function remove_query_strings_split($src) {
	//strip query strings
	$output = preg_split("/(&ver|\?ver)/", $src);
	return $output[0];
}