Is it possible to create Xcode widget in Xcode 12 but without the use of SwiftUI and instead use XIB files to construct the Widget UI?
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.