WordPress Admin: Hardcode max number of items per page.

hardcode-number-of-items.php

<?php

/**
 * name
 *
 * @package     Soderlind\MuPlugins\HardcodeNumberOfItems
 * @author      Per Soderlind
 * @copyright   2021 Per Soderlind
 * @license     GPL-2.0+
 *
 * @wordpress-plugin
 * Plugin Name: Hardcode number of items per page.
 * Description: Will set the number of items per page to max 20.
 * Version:     1.0.0
 * License:     GPL-2.0+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 */

declare( strict_types = 1 );
namespace Soderlind\MuPlugins\HardcodeNumberOfItems;

if ( ! defined( 'ABSPATH' ) ) {
	wp_die();
}

/**
 * Set the number of items per page to max 20.
 *
 * @param int $val Number of items per page.
 * @return int
 */
function __return_max_20( $val ) : int { // phpcs:ignore WordPress.NamingConventions.ValidFunctionName.FunctionDoubleUnderscore,PHPCompatibility.FunctionNameRestrictions.ReservedFunctionNames.FunctionDoubleUnderscore
	return ( $val > 20 ) ? 20 : $val;
}


add_filter( 'edit_category_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'edit_comments_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'edit_page_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'edit_post_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'edit_post_tag_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'plugins_network_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'plugins_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'site_themes_network_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'site_users_network_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'sites_network_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'themes_network_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'upload_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'users_network_per_page', __NAMESPACE__ . '\__return_max_20' );
add_filter( 'users_per_page', __NAMESPACE__ . '\__return_max_20' );