I don’t think the plugin has an option to display a menu in Classic Mode by default, but you could certainly override the existing templates in your theme or in a child theme.
That process is described in https://amp-wp.org/documentation/how-the-plugin-works/classic-templates/.
So what you can do is provide custom wp-content/themes/my-theme/amp/header.php and wp-content/themes/my-theme/amp/style.php files in your theme and display navigation menus using wp_nav_menu() in it. The style file is for adding the needed CSS for that menu.
Hope that helps!
Thanks Pascal,
I resolved this problem by copying templates folder from plugin to my theme root and add this in functions.php:
add_filter( 'amp_post_template_dir', 'lc_custom_amp_templates' );
function lc_custom_amp_templates() {
$file = dirname( __FILE__ ) . '/amp';
}
So now I can customize amp templates (add navigation) etc.