functions.php

<?php

add_action( 'template_redirect', __NAMESPACE__ . '\\hide_single_testimonials' );
/**
 * We don't want to show single testimonials, only the archive.
 *
 * If someone tries to visit a single testimonial this action will ping them back to the testimonials archive.
 *
 * @since 1.0.0
 */
function hide_single_testimonials() {
	if ( is_singular( [ 'me_testimonials' ] ) ) {
		wp_redirect( get_post_type_archive_link( 'me_testimonials' ), 301 );
		exit;
	}
}