How to propoerly use Category model?

[NowakAdmin]

Hi, i try to use this example no 3 of:
https://github.com/corcel/corcel#cats

// clean and simple all posts from a category
$cat = Category::slug('uncategorized')->posts->first();
$cat->posts->each(function($post) {
    echo $post->post_title;
});

but there is no model "Catergory" in this package or I can't find it.
I 've tried to change to "Taxonomy" or other classes but some methods were missing.

I tried:

use Corcel\Model\Post as Category;
use Corcel\Model\Taxonomy as Category;
use Corcel\Model\Builder\TaxonomyBuilder as Category;

But nothing works, also my VisualStudio have no advices for me there. So I tried to achieve same results using other way:

$cat = Taxonomy::where('term_id', 20)->with('posts')->get();

foreach ($cat->posts as $post) {
    echo $post->post_title
}

But it gives error:
Property [posts] does not exist on this collection instance.

It's probably my missunderstanding of how eloquent collection works or objects itself...

Or i need to make own model to handle it?
I also have a clue that probably I need to add something in config around:

  'post_types' => [
//        'video' => App\Models\Video::class,
    ],

Help me please.