Setting up GA4 integration in Shopify is not straightforward because you can only access the checkout liquid template code if you are on Shopify Plus. However, there might be an answer to setting up GA4 on Shopify using the new customer events just released in October 2022.
https://kevdees.com/how-to-install-ga4-on-shopify-using-customer-events-pixels-and-gtm/