You can customize your scene breaks in your theme settings under Scene Break.
You can make changes to your theme on the Formatting Tab by clicking the three dots next to the theme name and selecting Edit or Edit as New Theme.
For more details on how to set up or adjust your theme settings, you can refer to this tutorial: Create A Custom Theme. It provides detailed instructions and tips on creating and modifying your theme.
Note: The scene break settings will appear in the preview and your final exported files, however, when you return to the Writing Tab, you will still see the scene break placeholder.