Region In MKMapView Not Updating In onAppear

Hi. This is my MapView code

import SwiftUI
import MapKit

struct MapView: UIViewRepresentable {

  var region: MKCoordinateRegion
  var polylineCoordinates: [CLLocationCoordinate2D]?

  func makeUIView(context: Context) -> MKMapView {
    let mapView = MKMapView()
    mapView.delegate = context.coordinator
    mapView.region = region
    
    if let polylines = polylineCoordinates {
      let polyline = MKPolyline(coordinates: polylines, count: polylines.count)
      mapView.addOverlay(polyline)
    }
     
    return mapView
  }

  func updateUIView(_ view: MKMapView, context: Context) {
    
  }

  func makeCoordinator() -> Coordinator {
    Coordinator(self)
  }

}

class Coordinator: NSObject, MKMapViewDelegate {
  var parent: MapView

  init(_ parent: MapView) {
   self.parent = parent
  }
   
  func mapView(_ mapView: MKMapView, rendererFor overlay: MKOverlay) -> MKOverlayRenderer {
    if overlay is MKPolyline {
      let routePolyline = overlay as! MKPolyline
      let renderer = MKPolylineRenderer(polyline: routePolyline)
      renderer.strokeColor = UIColor.white
      renderer.lineWidth = 2
      return renderer
    }
    return MKOverlayRenderer()
  }
}

If i do this

var body: some View {
    MapView(region:  [array of CLLocationCoordinage2D])
    .edgesIgnoringSafeArea(.all)
}

it works since the value of the region property is set in the constructor. However, what i want is to set the region property in the onAppear closure. What is lacking here since it does not work.

I wish to do something like this

var body: some View {
    MapView(region:  region)
    .edgesIgnoringSafeArea(.all)
    .onAppear {
          region = [array of CLLocationCoordinage2D]
    }
}

I want to apply the same thing to polylineCoordinates property but for now, if I can make it work with region, I am sure the same thing can be applied to polylineCoordinates property.

Thoughts?