RuntimeBroker.exe seems to be a go-between for UWP accessing the file system.
Here is a UWP app button click done in c++/winrt. Just use it to open an entire drive or c:\program files and RuntimeBroker.exe can use more than a few gigs. Takes a very long time.
Windows::Foundation::IAsyncAction MainPage::ClickHandler(IInspectable const&, RoutedEventArgs const&)
{
std::wstring _debugMessage = L"ClickHandler started";
OutputDebugString(_debugMessage.data());
Windows::Storage::Pickers::FolderPicker _folderPicker;
_folderPicker.FileTypeFilter().Append(winrt::hstring(L"*"));
winrt::Windows::Storage::StorageFolder _folder = NULL;
_folder = co_await _folderPicker.PickSingleFolderAsync();
co_await winrt::resume_background();
auto _storageFiles = _folder.GetFilesAsync(Windows::Storage::Search::CommonFileQuery::OrderByName).get();
_debugMessage = std::to_wstring(_storageFiles.Size());
OutputDebugString(_debugMessage.data());
co_await winrt::resume_foreground(this->Dispatcher());
myButton().Content(box_value(L"Clicked"));
}
Runtimebroker.exe seems to hold about 60k per StorageItem held. It is probably therefore holding a thumbnail pic (just a guess), which is much bigger than many of the files. Horrendously inefficient.