CI4 - Extending Core System Class - HTTP/URI

When using new you have to be explicit about the namespace which can be done with use

PHP Code:

use App\Libraries\URI;

$uri = new URI(); 


Or it can be done with a fully qualified class name the way you did in app/config/services.php

PHP Code:

$uri = new \App\Libraries\URI(); 


Note the leading backslash in the above line of code.