Hi! Sorry to hear that your Sudoku app shows a black screen when you click on it. To help you better, could you tell me a bit more? For example, does the app open at all before going black, or does it just show a black screen immediately? Also, have you tried any steps so far like restarting your Mac or reinstalling the app?

In the meantime, I can suggest a few steps to try on your Mac OS X 10.15.7:

1. Quit and Restart the App
Make sure the Sudoku app is fully closed. You can do this by right-clicking its icon in the Dock and selecting "Quit" or by pressing Command + Q while the app is active.

2. Restart your Mac
Sometimes a simple restart resolves temporary glitches. Click the Apple menu and select “Restart.”

3. Check for App Updates
Go to the App Store and see if there’s an update available for the Sudoku app. Updates often fix bugs causing issues like black screens.

4. Reinstall the App
If the problem persists, try deleting the app and reinstalling it:
- Find the app in the Applications folder.
- Drag it to the Trash and empty the Trash.
- Re-download it from the App Store and install again.
Note: Reinstalling may erase some app data or progress, so if you have important game data, check if the app supports backups or syncing first.

5. Check for Display or Graphics Issues
Since the screen goes black, verify if other apps work fine. If you notice similar black screens in other apps, it may be related to your Mac’s graphics or display settings, not just the Sudoku app.

If these steps don’t help, please let me know more about the behavior and any error messages you see. I’m here to assist further! Are you ready to try these steps?