Creating a directly-executable cross-platform GUI app using Python involves using a tool called PyInstaller. PyInstaller allows you to bundle your Python code and its dependencies into a single executable file that can be run on any platform.

Here are the general steps to create a directly-executable cross-platform GUI app using Python and PyInstaller:

1. Install PyInstaller: You can install PyInstaller using pip. Open a terminal or command prompt and type pip install pyinstaller. This will install PyInstaller on your system.
2. Create your Python script: Write your Python code that creates the GUI for your app. Make sure that your code is cross-platform compatible.
3. Test your Python script: Test your Python code to make sure it works as expected.
4. Bundle your Python code using PyInstaller: Open a terminal or command prompt and navigate to the directory that contains your Python script. Type pyinstaller --onefile --windowed your_script_name.py and hit enter. This will create a single executable file that can be run on any platform.
5. Test the executable: Test the executable to make sure it works as expected on different platforms.
6. Distribute your app: Distribute your app to your users by sharing the executable file. Make sure to include instructions on how to install and run the app.

By following these steps, you can create a directly-executable cross-platform GUI app using Python and PyInstaller.