Using a Laravel factory to create a user and then update a relationship directly is possible using factory callbacks. Using a configure method you can call afterCreating and afterMaking closures:

<?php

namespace Database\Factories;

use App\Models\Tenant;
use App\Models\User;
use Illuminate\Database\Eloquent\Factories\Factory;
use Illuminate\Support\Facades\Hash;
use Illuminate\Support\Str;

class UserFactory extends Factory
{
    protected $model = User::class;

    public function definition(): array
    {
        return [
            'name'           => $this->faker->name(),
            'slug'           => Str::slug($this->faker->name()),
            'email'          => $this->faker->email(),
            'password'       => Hash::make('password'),
            'is_active'      => 1,
            'remember_token' => Str::random(10),
        ];
    }

    public function configure()
    {
        return $this->afterCreating(function (User $user) {
            $user->tenant_id = Tenant::factory()->create([
                'owner_id' => $user->id
            ]);
            $user->save();
        });
    }
}

Read more about Factory Callbacks