session not working?

Why you just not using :

Code:

$this->session->set_userdata()

 
Or for CI4

Code:

$session->set()

Before it you must call the session library.

Both ways work the same as i understand it, only difference between them being the CI session library has helper functions that makes things easier to do/work with.
 
In my case, I personally prefer pushing/deleting all my values to/from the $_SESSION variable (the way I learned way back in '03) and use the CI helper functions as needed.