Manual Install

...
When I run: http: // localhost: 8080 / ci4 / public
...

But using XAMPP (or something like that; I use XAMPP on Windows) I think you'd must run http: // localhost / ci4 / public
Additionally, I had to change $baseURL on app\Config\App.php from http: // localhost: 8080 to something like http: // localhost / ci4 / public

The base url can also be changed in the .env file, and it’s not necessarily localhost/ci4/public. It depends on how your configured your web server. It can be anything you decide, like http://my-awesome-website.test