Restrict dashboard access

/**
 * Restrict access to the administration screens.
 *
 * Only administrators will be allowed to access the admin screens,
 * all other users will be shown a message instead.
 *
 * We do allow access for Ajax requests though, since these may be
 * initiated from the front end of the site by non-admin users.
 *
 * @link https://developer.wordpress.org/reference/hooks/admin_init/
 */
function restrict_admin() {

    // Set user capability required to access dashboard.
    // List of standard capabilities here: https://wordpress.org/support/article/roles-and-capabilities/
    $required_capability = 'manage_options';
    
    if ( ! current_user_can( $required_capability ) && ( ! wp_doing_ajax() ) ) {
        wp_die( __( 'You are not allowed to access this part of the site' ) );
    }
}
add_action( 'admin_init', 'restrict_admin', 1 );