The biggest change is that \Setono\EditorJSBundle\Twig\Runtime::render(string $json): string was changed to \Setono\EditorJSBundle\Twig\Runtime::render(?string $json): string. This makes is a lot easier to do something like obj.property where property can be null and you don't want to test it.
Full Changelog: v1.2.0...v1.3.0