Those store would be on Shopify Plus plan as that is the only one you can change the checkout.
There's not an official statement but it does require to make it enable from shopify support.
Explain your issue to them and ask them to enable GA unsafe script on checkout page
Hello - I am setting up GTAG and running into some issues, as the setup is very confusing for Shopify.
We have a basic account, so we do not have access to checkout.liquid.
Can you please provide me the information as to where I should place my:
That is not guide - useless information just to get a link
I created a step by step guide for installing Google Tag Manager on Shopify here
Finally somebody explained it...
@CiprianSo that is because Shopify removed the option of adding any other code in the Additional GA scripts, BUT the actual GA code. GTM is not GA code, and this was a hack to accomplish having GTM on Checkout pages.
Upgrade to Shopify Plus and you'll have the ability to change Checkout pages as well