Edit file File name : block.json Content :{ "$schema": "https://schemas.wp.org/trunk/block.json", "apiVersion": 3, "name": "core/legacy-widget", "title": "Legacy Widget", "category": "widgets", "description": "Display a legacy widget.", "textdomain": "default", "attributes": { "id": { "type": "string", "default": null }, "idBase": { "type": "string", "default": null }, "instance": { "type": "object", "default": null } }, "supports": { "html": false, "customClassName": false, "reusable": false }, "editorStyle": "wp-block-legacy-widget-editor" } Save