To use anomyzizeIP with this plugin:

includes/templates/YOURTEMPLATE/jscript/jscript_ec_analytics.php

around line 29
change from

Code:
<?php
//global $analytics, $cID;
$cID = (isset($_SESSION['customer_id'])) ? "customerID#".$_SESSION['customer_id']:"guest";
echo ($cID === "guest") ? "ga('create', '".$trackingID."', 'auto') ;\n":"ga('create', '".$trackingID."', {'userId':'{$cID}'});\n";   
echo "ga('require', 'ec');\n"; 
echo "ga('require', 'displayfeatures');\n";
if (!isset($_SESSION['analytics'])) {  echo "ga('send', 'pageview');\n";}
to

Code:
<?php
global $analytics, $cID; 
$cID = (isset($_SESSION['customer_id'])) ? "customerID#".$_SESSION['customer_id']:"guest";
echo ($cID === "guest") ? "ga('create', '".$trackingID."', 'auto') ;\n":"ga('create', '".$trackingID."', {'userId':'{$cID}'});\n";
echo "ga('set', 'anonymizeIp', true); \n";     
echo "ga('require', 'ec');\n"; 
echo "ga('require', 'displayfeatures');\n";
if (!isset($_SESSION['analytics'])) {  echo "ga('send', 'pageview');\n";}
To be GDPR compliant you should also support the GA Opt-Out Cookie:

Integrate the following link to your privacy policy:

Code:
<a onclick="alert('Google Analytics has been disabled');"href="javascript:gaOptout()">Disable Google Analytics</a>
And integrate the following script somewhere in the head section in includes/templates/YOURTEMPLATE/common/html_header.php
(Change UA-1234567 to your own ID)

Code:
<script type="text/javascript">
var gaProperty = 'UA-1234567';
var disableStr = 'ga-disable-' + gaProperty;
if (document.cookie.indexOf(disableStr + '=true') > -1) { window[disableStr] = true;
}
function gaOptout() {
document.cookie = disableStr + '=true; expires=Thu, 31 Dec 2099 23:59:59 UTC; path=/';
window[disableStr] = true; }
</script>
The user ID is sent to Google Analytics but this does not contain any personal data so I' m not sure what should not be GDPR compliant doing so.