The checkout.liquid theme file is being deprecated
Shopify Plus merchants can now customize their in-checkout pages, which include their Information, Shipping, and Payment Pages, using checkout extensibility—an easier way to customize Shopify Checkout in a way that’s app-based, upgrade-safe, higher-converting, and integrated with Shop Pay. It lets merchants make code-free customizations to their checkout using the new checkout editor and public apps, while also giving them the flexibility to develop custom apps for more bespoke customizations.
Checkout extensibility replaces checkout.liquid. As a result, checkout.liquid customizations will no longer work for in-checkout pages starting August 13, 2024. Shops that currently use checkout.liquid to customize their in-checkout pages need to upgrade their customizations to checkout extensibility before this date. Checkouts that aren’t upgraded on time will be automatically upgraded to an un-customized, out-of-the-box Shopify Checkout.
Shopify Plus merchants can continue customizing their post-checkout pages, which includes the Thank You and Order Status Page, with checkout.liquid. However, we’ll eventually support customization on these pages with checkout extensibility as well.