// add class to body class on single post template
function themeprefix_body_class_blocks( $classes ) {
    if ( is_singular() && has_blocks() ) {
        $classes[] = 'made-with-gutenberg';
    }
    return $classes;
}
add_filter( 'body_class', 'themeprefix_body_class_blocks' );


// Add class to post classes in blog page or archive pages.
function themeprefix_post_class_blocks( $classes ) {
	if ( is_archive() || is_home() ) {
		if ( has_blocks() ) {
			$classes[] = 'made-with-gutenberg';
		}
	}
    return $classes;
}
add_filter( 'post_class', 'themeprefix_post_class_blocks' );