Accessing variable in function through object property throws illegal offset type

Question

I'm working with php, codeignitor 3 and groceryCRUD. I'm trying to get access to variables inside of a callback function of groceryCRUD and tried to set it as a property to the this object. I wanted to reset or renew it on every foreach loop iteration and expected to be able to access it inside of the function like shown below. Unfortunately this doesn't work and I get an error 'Illegal Offset Type'. Thanks for any help :)

public function somefunc(){
    ...
    $array = [['one', 'two'], ['one', 'two']];
    foreach ($array as $x) {
        $this->my_prop_var = $x;
        $crud->callback_column('column_name',
            function ($fieldValue) {
                echo $this->my_prop_var[0];
                return something... ;
             }
        );
                
        unset($this->my_prop_var);
    };


};