Laravel/Mongo Not updating integer key in database

I have this code in my old version of jenssegers / mongodb

$employee = Employee::findById($user_id, true);
$employee->{'38'} = 'Php';
$employee->save();

And was updating fine,
But now i have upgraded to the latest versions laravel-mongodb with php8.3 and Lumen 10
This code is not working insted it update the 0 index of record.
How to solve this problem. please suggest as i have a big database with numeric keys.
However i have tried these solutions

$employee['38'] = 'Php';
$employee->setAttribute('38', 'Php');

but nothing worked.