If you need to customize WordPress dashboard by editing it for specific use ID or based on the user role, you can easily add body class to the dashboard with this code, which you can put it in the function.php or create this plugin
<?php
/*
Plugin Name: Add User ID's dashboard
Plugin URI: https://programmeriz.rs
Description: Add user's id to the body class of the dashboard
Version: 0.1
Author: Milan Grujic
Author URI: https://programer.iz.rs
*/
add_filter('admin_body_class', function($classes) {
$current_user = wp_get_current_user();
$classes .= ' ' . 'user-id-' . $current_user->ID . ' ' . 'user-role-' . $current_user->roles[0] . ' ';
return $classes;
});
?>