[OBSOLETE] Update to Jetpack 8.4.2 to fix this issue.

amp-jetpack-admin-bar-workaround.php

<?php
/**
 * AMP Jetpack Admin Bar Workaround initialization file.
 *
 * @package   AMP_Jetpack_Admin_Bar_Workaround
 * @author    Weston Ruter, Google
 * @link      https://gist.github.com/westonruter/d168c290d6c01c107da960d48fa3dad3
 * @license   GPL-2.0-or-later
 * @copyright 2020 Google Inc.
 *
 * @wordpress-plugin
 * Plugin Name: AMP Jetpack Admin Bar Workaround
 * Plugin URI: https://gist.github.com/westonruter/d168c290d6c01c107da960d48fa3dad3
 * Description: Workaround for <a href="https://github.com/Automattic/jetpack/issues/15353">Automattic/jetpack#15353</a>.
 * Version: 0.3
 * Author: Weston Ruter, Google
 * Author URI: https://weston.ruter.net/
 * License: GNU General Public License v2 (or later)
 * License URI: http://www.gnu.org/licenses/gpl-2.0.html
 * Gist Plugin URI: https://gist.github.com/westonruter/d168c290d6c01c107da960d48fa3dad3
 */

namespace AMP_Jetpack_Admin_Bar_Workaround;

// Move up Jetpack AMP support initialization so we can unhook the show_admin_bar filter before other init actions run.
add_action(
	'plugins_loaded',
	function () {
		$priority = has_action( 'init', [ 'Jetpack_AMP_Support', 'init' ] );
		if ( false === $priority ) {
			return;
		}

		remove_action( 'init', [ 'Jetpack_AMP_Support', 'init' ], $priority );

		add_action(
			'init',
			function () {
				\Jetpack_AMP_Support::init();

				// Unhook the show_admin_bar filter added in Jetpack_AMP_Support::init().
				remove_filter( 'show_admin_bar', [ 'Jetpack_AMP_Support', 'show_admin_bar' ] );
			},
			-1
		);
	}
);

Jetpack v8.4.2 is now available which fixes this issue. Please update and uninstall this workaround plugin.