Load amp templates without plugin wordpress

functions.php

define( 'AMP_QUERY_VAR', 'amp' );
    
add_rewrite_endpoint(AMP_QUERY_VAR , EP_PERMALINK | EP_PAGES | EP_ROOT);

add_filter( 'template_include', 'amp_page_template',99 );

function amp_page_template( $template ) {

    if( get_query_var( AMP_QUERY_VAR , false ) !== false ) {

        if ( is_page( 'about-us' ) ) {
            $new_template = get_template_directory() .  '/amp-about-us.php';
            return $new_template;
        }
        
		if ( is_home() ) {

            $new_template = get_template_directory() .  '/amp-home.php';
            return $new_template;
        }
      
    }

    return $template;
}