I was created a boilerplate for integrating CodeIgniter 3 and Vue 3, and for the CodeIgniter 4 the idea is still the same.

You can found it here: https://github.com/ngekoding/codeigniter-vue-boilerplate

The main parts to make it works:

• application/helpers/vite_helper.php
• application/controllers/Vue.php
• application/config/routes.php
• application/views/index.vue.php
• frontend/vite.config.js

It is a basic configuration, I think you can easily fit it for your CodeIgniter 4.

Let me know if you still get any issue.