loading CI instance from helper?

Hi folks
I'm converting a CI3 project to CI4
My old project loaded in the CI3 instance like this from a site_helper I created

Code:

$CI =& get_instance();

and would then happily go about its business using all the usual libraries etc, like this

Code:

$get = $CI->input->get();
$home_url = $CI->config->item("home_url");

Etc.

However, this does not work in CI4.x

Is there a way to do this or am i barking up the wrong tree, I couldn't see anything about this in the online documentation.

Many thanks for any help

P