How to custom the RegisterController to save multiple data when user selected

Dear all,

I am a newbie in Laravel and I need your help.

I'm using the Laravel 7. I have 3 tables in my database.

1. User to save the registered users
2. Categories to show in the front-end that I provided for them to choose (multiple)
3. Vendor_Cat that I collecting the user_id and category_id after the user registered

Here are my Models

public function users(){
        return $this->BelongsToMany(User::class);
    }
public function categories(){
        return $this->BelongsToMany(Categories::class);
    }

And this is the Laravel RegisterController

   protected function create(array $data)
    {
        return User::create([
            'name' => $data['name'],
            'email' => $data['email'],
            'password' => Hash::make($data['password']),
            'tel' => $data['tel'],
            'lineid'=> isset($data['lineid']) ? $data['lineid'] : null,
        ]);

If I want to save the category Ids that I use @foreach to show in the Register Form after the users selected. What should I do?

Here is the explanation image https://ibb.co/vQpfxxH

p.s. sorry for my bad English.