You can use sys.get_application_path() to get the path to the application, but it requires special considerations per platform since sometimes it points you to the directory where the exe is and where your mygraphics.png will also be, and sometimes it points you to an .app folder which you must then go into like in macOS. iOS is flat I think.
For game.project you want something like
bundle_resources = /bundled
sys.load_resource is the wrong thing to use for bundle_resources. If you want to load something with sys.load_resource their folders should be listed under custom_resources, which are included packed inside of the game files. These files are relative to the root of your project. So if you have “/json/myfile.json” that’s the path you would use for loading, and you would want to include the json folder as a custom resource.
Usually you want to use budled resources when you want something outside of the game pack for various reasons such as reducing memory footprint like with FMOD sound banks, or swapable portal splash images.