Blog tutorial

Good afternoon, Everybody! I am learning Laravel and I went through the tutorial and now I am a bit stuck, so in short I defined class Post and which has a function All and function Find. in both cases when I dd returns I get all the information I need, but then when I call my class Post::find($slug) from routes/web.php I return Null. Has anybody got any ideas?

namespace App\Models;

use Illuminate\Database\Eloquent\ModelNotFoundException;
use Illuminate\Support\Facades\File;
use Spatie\YamlFrontMatter\YamlFrontMatter;
use Illuminate\Support\Facades\Cache;


class Post
{

    public $title;

    public $slug;

    public $date;

    public $excerpt;

    public $body;


    public function __construct($title, $body, $date, $excerpt, $slug)
    {
       $this -> title = $title;

       $this -> body = $body;

       $this -> date =  $date;

       $this -> excerpt = $excerpt;

       $this -> slug = $slug;


    }

    public static function all()
    {
       return cache()->rememberForever('posts', function() {
       return collect(File::files(resource_path("posts")))
        -> map(fn($file) => YamlFrontMatter::parseFile($file))
        -> map(fn ($document) => new Post(
                $document -> matter("title"),
                $document -> body,
                $document -> matter("date"),
                $document -> matter("excerpt"),
                $document -> matter("slug"),
            ))
            -> sortByDesc('date');

        });

    }
    public static function find($slug)
    {
        $posts = Post::all();
        $posts -> firstWhere('slug', $slug);



    }

}

use App\Models\Post;
use Illuminate\Support\Facades\Route;
use Illuminate\Support\Facades\File;


Route::get('/', function () {
    return view ('posts', [
        'posts' => Post::all()
    ]);

    });

Route::get('posts/{post}', function ($slug) {
        dd(Post::find($slug));
        return view ('post', [
        'post' => Post::find($slug)
    ]);

})->where('post', '[A-z_\-]+');