<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MyApp.MainPage"
             BackgroundColor="{DynamicResource SecondaryColor}">
    <Grid x:Name="RootGrid">
        <Label Text="Stuff"  />
    </Grid>
</ContentPage>

using Telerik.XamarinForms.Primitives;

namespace MyApp;

public partial class MainPage : ContentPage
{
    RadPopup popup;
    
    public MainPage()
    {
        InitializeComponent();

        popup = new RadPopup();
        popup.PlacementTarget = this;
        popup.Placement = PlacementMode.Center;

        popup.IsModal = true;
        popup.OutsideBackgroundColor = Color.FromArgb("#FF0000");

        popup.Content = new Label { Text = "Hello Telerik Popup!" };
    }
}

   at Telerik.RadMauiControlsHelper.<>c.<.cctor>b__0_0()
   at Telerik.RadMauiCoreHelper.get_MauiContext()
   at Telerik.XamarinForms.Primitives.RadPopup.SetPopupIsOpen(Boolean value)
   at Telerik.XamarinForms.Primitives.RadPopup.UpdatePopup()
   at Telerik.XamarinForms.Primitives.PopupBase.OnPlacementTargetChanged()
   at Telerik.XamarinForms.Primitives.PopupBase.<>c.<.cctor>b__113_3(BindableObject b, Object o, Object n)
   at Microsoft.Maui.Controls.BindableObject.SetValueActual(BindableProperty property, BindablePropertyContext context, Object value, Boolean currentlyApplying, SetValueFlags attributes, Boolean silent)
   at Microsoft.Maui.Controls.BindableObject.SetValueCore(BindableProperty property, Object value, SetValueFlags attributes, SetValuePrivateFlags privateAttributes)
   at Microsoft.Maui.Controls.BindableObject.SetValue(BindableProperty property, Object value, Boolean fromStyle, Boolean checkAccess)
   at Microsoft.Maui.Controls.BindableObject.SetValue(BindableProperty property, Object value)
   at Telerik.XamarinForms.Primitives.PopupBase.set_PlacementTarget(VisualElement value)