We use UIViewRepresentable to wrap the UIKit to be used in SwiftUI. Here is an example to wrap UIActivityIndicatorView

# ActivityIndicator.swift

import Foundation
import SwiftUI

struct ActivityIndicator: UIViewRepresentable {
    @Binding var isAnimating: Bool 
    
    func makeUIView(context: Context) -> UIActivityIndicatorView {
        let v = UIActivityIndicatorView()
        return v
    }
    
    func updateUIView(_ uiView: UIActivityIndicatorView, context: Context) {
        if isAnimating {
            uiView.startAnimating()
        } else {
            uiView.stopAnimating()
        }
        
    }
   
    typealias UIViewType = UIActivityIndicatorView
   
}

You only need create a file to implement the UIViewRepresentable protocol.

And here is how you use it

# ContentView.swift

struct ContentView: View {
 
    var body: some View {
        ActivityIndicator(isAnimating: .constant(true))
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Here is the result