juce::URL is intended for accessing webpages, I don’t know that it can be used to access local files.
If you want to load a file from disk, you should use
const auto cwd = juce::File::getCurrentWorkingDirectory();
const auto resourceFile = cwd.getChildFile ("Resource/Filename");
Alternatively, if you don’t want to have to ship your resource files separately to your app, you can mark them as binary resources in the Projucer and access them through the auto-generated
BinaryData namespace. For example, for an image:
const auto img = juce::ImageCache::getFromMemory (BinaryData::myImage_png,