Solution proposed by Ryan Davis to the problem described here https://twitter.com/lawiluk/status/1257661151258820608 . This sample is for MVVMCross but you should be fine with other Frameworks.

Forms2Native.cs

public class FormsTestView : BaseViewController<FormsTestViewModel>
{
    public override void ViewDidLoad()
    {
        base.ViewDidLoad();

        EdgesForExtendedLayout = UIRectEdge.None;

        Xamarin.Forms.Forms.Init();

        var page = new FormsTestPage { BindingContext = ViewModel };

        var formsViewController = page.CreateViewController();
        var nativeView = formsViewController.View;

        nativeView.TranslatesAutoresizingMaskIntoConstraints = false;
        formsViewController.WillMoveToParentViewController(this);
        formsViewController.ViewWillAppear(true);

        View.Add(nativeView);
        nativeView.LeftAnchor.ConstraintEqualTo(View.LeftAnchor).Active = true;
        nativeView.TopAnchor.ConstraintEqualTo(View.TopAnchor).Active = true;
        nativeView.RightAnchor.ConstraintEqualTo(View.RightAnchor).Active = true;
        nativeView.BottomAnchor.ConstraintEqualTo(View.BottomAnchor).Active = true;

        formsViewController.ViewDidAppear(true);
        formsViewController.DidMoveToParentViewController(this);
    }
}