codeigniter 4.1.1 update +1 problem

There's an example in the user guide almost identical to your code. But they are using the Query Builder functions. The Model class also call the query builder, so I'm not sure why it was not working for you.

From https://codeigniter.com/user_guide/datab...ating-data

PHP Code:

$builder->set('field', 'field+1', false);
$builder->where('id', 2);
$builder->update();
// gives UPDATE mytable SET field = field+1 WHERE `id` = 2