How can I use findAll with select in model?

Code:

// Method inside your controller

    public function dbtest()
    {
        $model = model('MyModel');
        
        $builder = $model->builder();
        $builder->select('column1, column2');

        $result = $model->findAll();
        var_dump($result);        
    }

This is tested and produces a result set without error.

However, after getting your code to work you would be better off creating a method in your model and returning your results rather than manipulating the database logic from within your controller.