Demonstration of how plugin land deals with deprecations while supporting multiple versions of WordPress.

shim.php

<?php
/**
 * Shim to account for WordPress 5.8 changes to widgets screen.
 * 
 * This code was written to avoid the block widgets screen from throwing
 * notices in WordPress 5.8 while allowing custom block plugins to support
 * WordPress 5.1 and earlier.
 * 
 * The original gist was a private gist with identifying information of the 
 * the plugin I was working on for my employer at the time. I've republished
 * it as a public gist with the identifying information removed.
 * 
 * At the time it was republished it's not really needed any more but it's
 * purpose is to demonstrate the lengths needed to go to in plugin land to
 * deal with changes to the block editor.
 * 
 * This discussion is taking place in the gutenberg repo:
 * https://github.com/WordPress/gutenberg/issues/55401
 * 
 * If your plugin still supports WordPress 5.1 you may need it but only
 * one of the ten most popular plugins do that so you can probably drop
 * support for yours too :)
 */

namespace PWCC\AvoidPhpNoticeOnBlockWidgetsScreen;
 

function editor_shim() {
	// Get a clean copy of $wp_version in to the local scope.
	require_once ABSPATH . WPINC . '/version.php';

	/*
	 * Shim to allow plugin to support WP versions prior to 5.2.
	 *
	 * In WordPress 5.2 a number of components were relocated from
	 * @wordpress/editor to @wordpress/block-editor with @wordpress/editor
	 * providing backward-compatibility support.
	 *
	 * In WordPress 5.8 the widgets screen started throwing a notice
	 * if @wordpress/editor was used to enable support of WordPress 5.1
	 * and earlier.
	 *
	 * @link https://github.com/WordPress/gutenberg/issues/33576
	 * @link https://core.trac.wordpress.org/ticket/53437
	 * @link https://make.wordpress.org/core/?p=41500
	 */
	wp_register_script(
		'pwcc-block-editor-package-shim',
		false,
		version_compare( $wp_version, '5.2.0', 'lt' ) ? [ 'wp-editor' ] : [ 'wp-block-editor' ],
		'1.0.0',
		true
	);

	wp_add_inline_script(
		'pwcc-block-editor-package-shim',
		'window.pwccBlockEditorShim = wp.blockEditor || wp.editor;'
	);

	wp_enqueue_script(
		'pwcc-plugin-editor-script',
		plugins_url( 'usage.js', __FILE__ ),
		[ 'pwcc-block-editor-package-shim' /* other deps */ ],
		'1.0.0',
		true
	)
}

add_action( 'enqueue_block_editor_assets', __NAMESPACE__ . '\\editor_shim' );

usage.js

import {
	FontSizePicker,
	ToggleControl,
	PanelBody,
} from '@wordpress/components';
import { __ } from '@wordpress/i18n';

/*
 * @TODO: Import from block-editor instead.
 *
 * This will require bumping the minimum supported version of WP to
 * WordPress 5.3 (released late 2019) once done.
 */
const {
	InspectorControls,
	PanelColorSettings,
	RichText,
} = window.pwccBlockEditorShim;