eatvio-infra/database/seeders/PlanAuthor.php

<?php

namespace Database\Seeders;

use App\Models\Plan;
use App\Models\User;
use Illuminate\Database\Seeder;

class PlanAuthor extends Seeder
{
    /**
     * Run the database seeds.
     */
    public function run(): void
    {
        if (User::count() > 0 && Plan::count() > 0) {
            Plan::each(function ($plan) {
                User::inRandomOrder()
                    ->first()
                    ->author_of_plans()
                    ->attach($plan->id);
            });
        }
    }
}