Gist for my tutorial: Building a Gutenberg sidebar plugin Part 3: Registering with the block editor. https://vanaf1979.nl/building-a-gutenberg-sidebar-plugin-part-3-registering-with-the-block-editor/

metatags-sidebar.js

/**
 * External dependencies.
 */
import React from 'react'

/**
 * WordPress dependencies.
 */
const { __ } = wp.i18n;
const { Fragment } = wp.element;
const { PluginSidebarMoreMenuItem, PluginSidebar } = wp.editPost;


/**
 * Sidebar component voor the gutenberg editor.
 */
class Sidebar extends React.Component {
    
    constructor() {

        super()

    }


    render() {

        return (
            <Fragment>

                <PluginSidebarMoreMenuItem target="metatags-sidebar" icon='editor-customchar'>

                    {__("MetaTags", "metatags")}

                </PluginSidebarMoreMenuItem>

                <PluginSidebar name="metatags-sidebar" title={__("MetaTags", "metatags")} >

                    <div className="metabox-sidebar-content">

                        <h3>Metatags</h3>
                        
                    </div>

                </PluginSidebar>

            </Fragment>
        )

    }

}


export default Sidebar