You can check to see if you have migrated your store to use Shopify's app block compatible post-purchase pages by visiting Shopify Admin > Settings > Checkout.
There will be a warning at the top of this page if you HAVE NOT yet migrated your store to use Shopify's app block compatible post-purchase pages.
Here is how the top of that page will appear if your store's post-purchase pages ARE compatible with app blocks:
To learn more about how easy Google Customer Reviews works with app block compatible post-purchase pages, please take a look at our article that explains how the survey opt-in pop-up works with app block compatible post-purchase pages.