Google Tag Manager – Reduce JavaScript execution time

If you add the following line to functions.php in your theme WP Rocket will be able to delay all of the GTM Kit scripts including the the GTM container:
add_filter('gtmkit_header_script_attributes', '__return_empty_array' );

Do you mean in Child theme ?

yes

and where exactly do i need to add this code?

in functions.php. If you do not have functions.php in you child theme, you must create the file and enter:

<?php

add_filter('gtmkit_header_script_attributes', '__return_empty_array' );

Hi, I have added this code to functions.php but there has been no changes.

Have you cleared all cache?

After clearing cache its looking lot better.

Your score is now 65: https://pagespeed.web.dev/analysis/https-www-myithub-com-au/01cr1xsa69?form_factor=mobile

Can I close this?

Yes thanks