Laravel 8, Model factory class not found

If you upgraded to 8 from a previous version you are probably missing the autoload directive for the Database\Factories namespace in composer.json:

"autoload": {
    "psr-4": {
        "App\\": "app/",
        "Database\\Factories\\": "database/factories/",
        "Database\\Seeders\\": "database/seeders/"
    }
},

You can also remove the classmap part, since it is no longer needed.

Run composer dump after making these changes.

Laravel 8.x Docs – Upgrade Guide – Database – Seeder and Factory Namespace