Cant use format on dateTime because it is a string?

First, I am just trying to show an input with date

  <input type="date" wire:model="sprintStartDate"/>

I set the variable sprintStartDate with this

$this->sprintStartDate = $this->sprint->date_start->format('Y-m-d');

I get this error Call to a member function format() on string

https://flareapp.io/share/o7A48zEP#F61

When I dd($this->sprint->date_start); , I get ^ "2022-06-24 18:09:17"

In the migration date_start is set too

$table->dateTime('date_start')->nullable();

in the factory I seed it with

date_start' => $this->faker->dateTimeBetween('-5 days', '-2 days'),

My Confusion

When I use $sprint->created_at it does work properly, but isn't created_at and updated_at also dateTimes? How come it won't work when I create my own column with the type of dateTime?