When registering the block in plugins\gravityforms\assets\js\dist\scripts-admin.min.js, the apiVersion needs to be change from version 2, to version 3. Version 2 breaks the iframe in the block editor. See When does the Block Editor get iFramed? · Issue #53511 · WordPress/gutenberg · GitHub
The product team has addressed this issue and a fix will be available in an upcoming major version.