GDPR: How to enable the IP Anonymization feature in Google Analytics?

Add after Google Analytics ID:

{ 'anonymize_ip': true }

So the script will look like this:

<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src="https://www.googletagmanager.com/gtag/js?id=GA_TRACKING_ID"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', 'GA_TRACKING_ID', { 'anonymize_ip': true });
</script>