If, for any reason, you need to get the fillable fields from a Laravel model, it's pretty straightforward.
Here's the first way you're able to achieve this:
$model = new User();
dd($model->getFillable());
This returns an array of all the fillable columns.
But we can do better. You can inline it like this:
dd((new User)->getFillable());
And from PHP 8.4, you won't need to parenthesize the instantiation of the model, so you'll be able to do this:
dd(new User()->getFillable());
Perhaps a neater solution is resolving the model out of the container first. Here's what that looks like:
dd(app(Model::class)->getFillable());
So, there are a bunch of ways to get the fillable columns you've defined in your models — all these examples do the same thing. Just choose which fits your style best.