Editor role to edit Menus – add_cap() works, but does not add menu item

Hello,
I’ve used the following to add the “edit_theme_options” capability to the Editor role:

$role_object = get_role( 'editor' );
$role_object->add_cap( 'edit_theme_options' );

This works fine, but I am unable to see the “Menus” item under Appearance. I can navigate directly to the page when logged in as an Editor (/wp-admin/nav-menus.php) and it works fine. I tried adding the “Menus” item back under Appearance manually using:

add_submenu_page('themes.php', 'Menus', 'Menus', 'edit_theme_options', 'nav-menus.php');

This also works, but once doing so, the missing menu items under Appearance suddenly appear, so now there are two “Menus” items.

Any ideas what I may be doing wrong? This used to work in previous version of WordPress.