If you can't get the $dates mutator to work (https://laravel.com/docs/6.x/eloquent-mutators#date-mutators), I think this would be a good use case for manual mutators and accessors.

Essentially a mutator manipulates the value going in and an accessor manipulates the value coming out.

So

// mutator
public function setCreatedAtAttribute($date) {
    $this->attributes['created_at'] = Carbon\Carbon::parse($date)->format('Ymd H:i:s');
}

// accessor
public function getCreatedAtAttribute($date) {
    return Carbon\Carbon::parse($date)->format('Y-m-d H:i:s');
}

There's also date casting in some later versions of Laravel https://laravel.com/docs/6.x/eloquent-mutators#date-casting

Use carbon to format dates

In the model

    Use Carbon\Carbon;

The format the retrieved dates

Carbon is deprecated in Laravel 6

@parthkundariya Do you have supporting evidence that Carbon is deprecated in Laravel 6? It is still in the framework composer, it is installed on all of my new Laravel 6 projects and there hasn't been any notifications that it would be deprecated.

Just seeing if there is something I (and the community) missed.

Have you tried on your models

    protected $dateFormat = 'Y-d-m H:i:s.v';

I used MSSQL on my last laravel project. Was using 5.8 tho. But that should work