Crud/CakePHP: placing findMethod in the controller

I am referring to this documentation:
https://crud.readthedocs.io/en/latest/actions/index.html#findmethod

Is there a way to place the find method in the controller, instead in App\Model\Table?

What I want to achieve:
I want to apply a filter in the index action, depending on some conditions. This means for example, that the pagination for Users should show only users whose name begins with a specific letter and this letter will be provided when the page is refreshed and will always change.

If it's not possible, is there a way I can apply this filter before any data is loaded from the database?

I tried this code in UsersController.php, but the table shows always all rows. I apparently don't understand how it works.

public function index()
{
    $users = $this->paginate($this->Users->find()->where(["id" => 1] ));
    $this->set(compact("users"));
    return $this->Crud->execute();
}

But, when - for testing - I use an unknown field in the where condition [for example bar] then I get this - correct - error message:

Column not found: 1054 Unknown column 'bar' in 'where clause'

So, apparently, the where condition is applied but for some reasons all rows are returned instead of only 1 row with id = 1. What am I missing?

UPDATE:
After having a look into the source code I see that the string find is set as prefix for the finder method name, so any other scope is not possible. Maybe in an update this could be considered.

So, now I have these 2 possibilites:

1. Adding it into the Table file.
2. Setting a filter in the Controller, but this I still didn't figure out how it works. Even I set it in beforePagination in the $event using setData( "query", $this->Users->find()->where( ["id" => 1]) this gets ignored.

Solution for question #2:

In UsersController.php in the index() method add this:

$this->Crud->on('beforePaginate', function(\Cake\Event\EventInterface $event) {
   $this->paginate ['conditions']['id'] = <the-id>;
});