const splitted = arr.reduce((acc, cur) => {
  const { dt } = cur;
  return { ...acc, [dt]: [...(acc[dt] || []), cur] };
}, {});
const result = Object.values(splitted); // если надо массив

$key = 'Model';
$result = [];
if (key_exist($key, $arr)) {
    $keyVal = $arr[$key];
    $result[$keyVal] = $arr;
    unset($result[$keyVal][$key]);
}