replace a taxonomy template with a rendered post template

Paul.php

<?php
/**
 * Plugin Name: Render a specific Post on a Taxonomy archive page.
 * Plugin Author: Paul Gibbs.
 * License: public domain
 */

namespace paul;

use WP_Post;

// Change this to a POST that exists!!
const TAX_GUTENBERG_POST_REPLACEMENT_ID = 45;

/**
 * Replace category/taxonomy archive template with a Post template.
 *
 * See: get_taxonomy_template() -> get_query_template()
 */
add_filter( 'template_include', function( $template ) {

	if ( ! is_category() ) {
		// You might need to check is_tax() here as well?
		return $template;
	}

	$gutenberg_post = get_post( TAX_GUTENBERG_POST_REPLACEMENT_ID );

	// If more tweaks are needed here, BuddyPress' bp_theme_compat_reset_post() may inspire.
	global $wp_query;
	$wp_query->post       = $gutenberg_post;
	$wp_query->post_count = 1;                    // Prevent comments form from appearing.
	$wp_query->post_type  = 'post';
	$wp_query->posts      = [ $wp_query->post ];
	$wp_query->is_archive = false;
	$wp_query->is_single  = true;
	$wp_query->is_tax     = false;

	// Load theme's single post template.
	return locate_template( [ 'singular.php' ] );
} );