WordPress Client Role Plugin - Create a user role similar to Admin and revokes specific capabilities.

client-role-plugin.php

<?php
/**
 * Plugin Name: Client Role Plugin
 * Plugin URI: https://gist.github.com/philhoyt/54a4a4e5a48d8cb0beb20edf1ba1ae51
 * Description: Adds a 'Client' user role and revokes certain capabilities from it.
 * Version: 1.0.0
 * Author: Your Name
 * Author URI: https://philhoyt.com/
 * License: GPL-2.0+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 */

defined( 'ABSPATH' ) || exit; // Prevent direct access to this file.

/**
 * Main plugin class.
 */
class Client_Role_Plugin {

	/**
	 * Initializes the plugin.
	 */
	public function __construct() {
		add_action( 'init', array( $this, 'add_client_role' ) );
		add_action( 'init', array( $this, 'revoke_client_capabilities' ), 10 );
	}

	/**
	 * Adds a 'Client' user role.
	 */
	public function add_client_role() {
		global $wp_roles;

		if ( ! isset( $wp_roles ) ) {
			$wp_roles = new WP_Roles();
		}

		// Adding a 'new_role' with all admin caps.
		$capabilities = get_role( 'administrator' )->capabilities;
		$wp_roles->add_role( 'client', 'Client', $capabilities );
	}

	/**
	 * Revokes capabilities for the 'Client' user role.
	 */
	public function revoke_client_capabilities() {
		$caps_to_remove = array(
			'update_core',
			'activate_plugins',
			'install_plugins',
			'update_plugin',
			'edit_plugins',
			'edit_themes',
			'export',
			'import',
			'create_users',
			'manage_options',
			'switch_themes',
		);

		$custom_role = get_role( 'client' );

		foreach ( $caps_to_remove as $cap ) {
			$custom_role->remove_cap( $cap );
		}
	}
}

new Client_Role_Plugin();