Add Google Tag Manager to Wordpress and Load Only If An Admin is NOT Logged In

functions.php

<?php // do not copy this line and make sure to replace "XXXXXXX" with your tag manager ID


// add Google Tag Manager after opening body tag on wordpress (part 1)
add_action( 'wp_head', 'add_custom_google_tag_manager_1', 1 );
function add_custom_google_tag_manager_1() {
	
	// if user is not a logged in admin then load gtm script tag
	if( !current_user_can('administrator') ) { 
	
	    //* replace XXXXXXX with your GTM tracking ID
	    ?><!-- Google Tag Manager --><script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
		new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
		j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
		'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
		})(window,document,'script','dataLayer','GTM-XXXXXXX');</script><!-- End Google Tag Manager --><?php
	}
	
}

//* add Google Tag Manager after opening body tag on wordpress (part 2)
//* If using genesis replace hook with genesis_before eg. add_action( 'genesis_before', 'add_custom_google_tag_manager_2', 1 );
add_action( 'wp_body_open', 'add_custom_google_tag_manager_2', 1 );
function add_custom_google_tag_manager_2() {
	
	// if user is not a logged in admin then load gtm noscript tag
	if( !current_user_can('administrator') ) {
		
	//* replace XXXXXXX with your GTM tracking ID
    ?>	  
<!-- Google Tag Manager (noscript) -->
<noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-XXXXXXX"
height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
<!-- End Google Tag Manager (noscript) -->  
	<?php
		
	}
}

Note - this works for MOST wordpress themes. But it assumes that the theme did not strip out the wp_body_open hook, which is required for the second part of GTM tagging to fire immediately after opening tag.