I am experiencing the same issue with Xcode 16.0. I have tested my widget on iOS 15-18 simulators and iOS 15 and 18 physical devices. The widget only disappears on iOS 15.

With iOS 15 and Xcode 16.x, widgets cannot be found in the widget list when the main app is running, and the poster's error occurs when widget targets are run. The problem still occurs with Xcode 16.1.

The reason I'm asking: During the transition, the rounded corner disappears at the final moment, creating a visible delay, which feels odd. In particular, some UI elements are clipped by the rounded corners, making the animation feel visually inconsistent or even awkward.

When the new Xcode can't download simulators, it's usually a permissions issue. Solution: Set the new Xcode as default: sudo xcode-select -s /Applications/Xcode.app/Contents/Developer Download iOS platform with sudo: sudo xcodebuild -downloadPlatform iOS If your Xcode isn't installed in the default path, update the path in step 1 to your actual installation location. This resolves the write permission issue for new simulators.

When the new Xcode can't download simulators, it's usually a permissions issue. Solution: Set the new Xcode as default: sudo xcode-select -s /Applications/Xcode.app/Contents/Developer Download iOS platform with sudo: sudo xcodebuild -downloadPlatform iOS If your Xcode isn't installed in the default path, update the path in step 1 to your actual installation location. This resolves the write permission issue for new simulators.