For those who prefer working with real data, you can set up your factory like this:

TalkFactory :

public function definition(): array
    {
        return [
            'user_id' => User::factory(),
            'title' => fake()->catchPhrase().' Talk',
            'length' => rand(15, 60),
            'type' => fake()->randomElement(TalkType::cases())->value,
            'abstract' => fake()->realText(),
            'organizer_notes' => fake()->realText(),
        ];
    }

ConferenceFactory :

public function definition(): array
    {
        $startsAt = now()->addMonths(6);
        $endsAt = $startsAt->clone()->addDays(3);
        $cfpStartsAt = $startsAt->clone()->subMonths(4);
        $cfpEndsAt = $cfpStartsAt->clone()->addMonths(2);

        return [
            'title' => fake()->country().' Conference',
            'location' => fake()->address(),
            'description' => fake()->realText(),
            'url' => fake()->url(),
            'starts_at' => $startsAt,
            'ends_at' => $endsAt,
            'cfp_starts_at' => $cfpStartsAt,
            'cfp_ends_at' => $cfpEndsAt,
        ];
    }

P.S. This is just an example, but you can easily distinguish between a talk and a conference.

Databases, Models, Factories, and Seeders