Xcode 12 iOS 14 Widget without SwiftUI

No, due to performance and battery life concerns, WidgetKit only works with SwiftUI.

https://developer.apple.com/documentation/widgetkit

You configure the widget with a timeline provider, and use SwiftUI views to display the widget’s content. The timeline provider tells WidgetKit when to update your widget’s content.

Widget protocol is only available in SwiftUI framework, so you can only create widgets using SwiftUI.

https://developer.apple.com/documentation/swiftui/widget

Update

You can't use UIKit views wrapped in UIViewRepresentable within SwiftUI for Widgets, It will appear blank.

https://developer.apple.com/forums/thread/653471