If you're having trouble finding Nukebound in the level browser, you can also download it from the Geometry Dash website. Here's how:
is not a separate game or app to download, but rather a community-created event and level series within the official Geometry Dash game Geometry Dash Nukebound Download Ios
Here is the guide on what this likely is and how to get it on iOS. If you're having trouble finding Nukebound in the