As of 2023-10-24, the order status page is getting a new look with updated visual treatment that is consistent with new customer accounts. This change will be rolling out progressively to all developer shops on checkout extensibility developer preview to ensure a smooth transition.
To view this change in developer shops on the checkout extensibility developer preview, navigate to Settings > Checkout > Customize and select Order Status from the page dropdown.
No action is required and there should be no changes to any UI extensions in development.
Learn more about UI extensions on the thank you and order status pages on Shopify.dev.