Please indicate exact path for default.php please?After you have created the override then path should be :
[joomla_root]/templates/your_template_name/html/mod_whatsapp_agent/default.php
Also on an unrelated question, you indicate that the changes will survive update. Will they also be valid whenever we decide to transition from 3.10 to Joomla 4?
if($watarget == 0){ $clickdirect = 'onClick="parent.location=\'https://'.$waurl.'.whatsapp.com/send?phone='.$item->agent_phone_number.'\'"'; }else{ $clickdirect = 'onClick="parent.open(\'https://'.$waurl.'.whatsapp.com/send?phone='.$item->agent_phone_number.'\')"'; }
if($watarget == 0){ $clickdirect = 'onClick="parent.location=\'https://wa.me/send?phone='.$item->agent_phone_number.'\'"'; }else{ $clickdirect = 'onClick="parent.open(\'https://wa.me/send?phone='.$item->agent_phone_number.'\')"'; }
if ((/Firefox[\/\s](\d+\.\d+)/.test(navigator.userAgent)) && (window.navigator.userAgent.indexOf("Windows")!= -1) ) { var URL = "https://web.whatsapp.com/send?phone="; }else { var URL = "https://<?php echo $waurl;?>.whatsapp.com/send?phone="; }
if ((/Firefox[\/\s](\d+\.\d+)/.test(navigator.userAgent)) && (window.navigator.userAgent.indexOf("Windows")!= -1) ) { var URL = "https://wa.me/send?phone="; }else { var URL = "https://wa.me/send?phone="; }