Add metabox to document tab in gutenberg

How can I add custom metabox in document tab in gutenberg?

There is documentation about adding plugin sidebar here, but I’m looking for adding custom metabox in existing document tab.

Here is the solution. Hope it will help you

const { registerPlugin } = wp.plugins;
const { PluginDocumentSettingPanel } = wp.editPost;

const MyDocumentSettingTest = () => (
        &ltPluginDocumentSettingPanel className="my-document-setting-plugin" title="My Panel"&gt
            &ltp>My Document Setting Panel&lt/p>
        &lt/PluginDocumentSettingPanel>
    );

registerPlugin( 'document-setting-test', { render: MyDocumentSettingTest } );

https://github.com/WordPress/gutenberg/blob/master/packages/edit-post/src/components/sidebar/plugin-document-setting-panel/index.js#L86