Redirects Any Category, Tag or Other Archive Page To The Single Posts When Only One Post In Archive

functions.php

function redirect_to_single_post(){

global $wp_query;
 
if( is_archive() && $wp_query->post_count == 1 ):

the_post();
        
$post_url = get_permalink();
        
wp_redirect( $post_url );

endif;
 
} 
add_action('template_redirect', 'redirect_to_single_post');