Adding post date to posts

Hello!

I'd like to include the post date on my posts. I've updated the customization/layout/blog sections on archives and single. I'm seeing the post date in the archive, but not on my single posts. I have previously requested help to display the categories and tags on the top of my posts and I think there might be some interference here. here's the PHP I was given that's running on my site:

add_filter( 'generate_header_entry_meta_items', function($item) {
   if (is_single()) {
      return array(
		  'post_date',
        'categories',
		'tags'
      );
   }
	return $item;
} );

(I think I added "post_date" myself to try and fix it, which didn't work)

Thanks!

Edit to add post example: https://www.remembryo.com/rct-finds-no-change-in-birth-rates-for-standard-or-era-timed-euploid-transfer/