I'm experiencing a very similar situation where my widgets are partly rendering UI elements with Xcode 12.1 and iOS 14.1 simulators. Some show most elements, some hardly anything. I rolled back to Xcode 12.0 and iOS 14.0 and my widgets display normally, and my physical SE 2020 iOS 14.1 device renders correctly.

Same. Tried uploading with Xcode 12/11.6, and via Transporter. Edit: And on a second Macbook