This code snippet modifies The SEO Framework plugin to let search engines index empty category archives by disabling the noindex directive. Note: WordPress may still emit a 404 response.

tsf-allow-empty-category-indexing.php

<?php
// Do not open PHP if PHP is already opened.


add_filter( 
	'the_seo_framework_enable_noindex_no_posts', 
	function ( $noindex ) {

		if ( is_category() ) {
			// To allow indexing, so set noindex to false.
			$noindex = false;
		}

		return $noindex;
	},
);