You can customize the mail message by using the VerifyEmail::toMailUsing method as outlined in Laravel docs.

https://laravel.com/docs/11.x/verification#customization

use Illuminate\Auth\Notifications\VerifyEmail;
use Illuminate\Notifications\Messages\MailMessage;

/**
 * Bootstrap any application services.
 */
public function boot(): void
{
    // ...

    VerifyEmail::toMailUsing(function (object $notifiable, string $url) {
        return (new MailMessage)
            ->subject('Verify Email Address')
            ->line('Click the button below to verify your email address.')
            ->action('Verify Email Address', $url);
    });
}