An example of how to set the Custom Message Templates list table to have the 'Name' column as a sortable column.

tw_ee_messages_sortable_columns.php

<?php // Do not include the opening PHP tag if you already have one.

add_filter('FHEE_manage_event-espresso_page_espresso_messages_sortable_columns', 'tw_ee_messages_sortable_columns', 10, 2);
function tw_ee_messages_sortable_columns($sortable, $screen) {
	if( $screen === 'espresso_messages_custom_mtps'){
		$sortable['messenger'] = ['MTP_messenger' => false];
		$sortable['name'] = ['MTP_name' => true];
	}
	return $sortable;
}