The dirt screens you’re seeing are the “World Loading” and “Generic Dirt Message” screens that close instantly, so you can’t edit their background the usual way while they’re running. To customize them you first need to open a persistent dummy instance of the screen:
- In the menu bar go to Tools → Dummy Screen Instances.
- Left‑click the entry for the dirt screen (there’s one for the level/world loading screen and one for the generic dirt message).
- That keeps the screen open so you can enable customization, create a layout for it, and right‑click the editor background to Set Background (or add an image element) just like on any other screen.
Once you’ve edited and saved that layout, the new background will appear each time the dirt screen shows up. Check the World Loading Screens guide for the full workflow: World Loading Screens. 😊