"config": {
  "platform": {
    "ext-pcntl": "7.3",
    "ext-posix": "7.3"
  }
}

https://newbedev.com/how-can-i-solve-laravel-horizon-v1-1-0-requires-ext-pcntl-the-requested-php-extension-pcntl-is-missing-from-your-system