Hello! I’m sorry to hear that your Sudoku.com app screen goes blank. Let's try to get to the bottom of this together. To start, could you tell me:

- Are you using the Sudoku.com app or the website on Safari or another browser?
- Does the blank screen appear right after starting the app or midway through a game?
- Have you noticed if this happens after an app update or macOS update?
- Have you tried any steps so far like restarting the app or your Mac?

This info will help me offer the best tailored advice for your Mac OS X 10.15.7 system.

In the meantime, here are some initial steps you can try:

1. Force quit and restart the Sudoku app or browser: Press Command + Q to quit the app completely, then reopen it. If you are on Safari, close the tab and open a new one.

2. Clear app or browser cache: Sometimes corrupted cache can cause display issues. For Safari, go to Safari > Preferences > Privacy > Manage Website Data, then remove data for Sudoku.com.

3. Check for software updates: Ensure your macOS and Sudoku app are updated to the latest versions available.

4. Disable browser extensions if using Safari that might interfere with the display.

5. Check your internet connection: A spotty network might cause the game assets not to load, resulting in a blank screen.

If the problem persists after these, it could be related to how the app renders graphics on your OS version or an account-specific issue.

Let me know what you find or if you want me to guide you step-by-step through any of these!