There is a little difference between TelerikUI popup and MAUI popup when Screen Resolution changed.

<?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"
             xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui"
             x:Class="MauiApp5.MainPage">

    <StackLayout Margin="0, 40, 0, 0">
        <Button Text="Open Popup" Clicked="Button_Clicked"/>
    </StackLayout>

    <!-- the popup is attached to the page -->
    <telerik:RadPopup.Popup>
        <telerik:RadPopup x:Name="popup"
                                    Placement="Center">
            <telerik:RadBorder CornerRadius="8"
                                     BackgroundColor="#93D7FF" 
                                     WidthRequest="250" 
                                     Padding="10">
                <Grid>
                    <Grid.RowDefinitions>
                        <RowDefinition Height="30" />
                        <RowDefinition Height="50" />
                        <RowDefinition Height="30" />
                    </Grid.RowDefinitions>
                    <Label Text="ACCEPT TERMS" />
                    <Label Grid.Row="1"
                       Text="By checking this, you agree to the Terms of Service and Privacy Policy." />
                    <Button Grid.Row="2"
                        Padding="2" 
                        HorizontalOptions="Start" 
                        Text="Agree &amp; Continue" 
                        Clicked="Button_Clicked1" 
                        CornerRadius="6"
                        BackgroundColor="#7A9BFF"
                        TextColor="White"/>
                </Grid>
            </telerik:RadBorder>
        </telerik:RadPopup>
    </telerik:RadPopup.Popup>

</ContentPage>

<?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"
             xmlns:telerik="http://schemas.telerik.com/2022/xaml/maui"
             x:Class="MauiGA.MainPage"
             x:Name="HomePage">
    <ContentPage.Resources>
        <DataTemplate x:Key="PopupTemplate">
            <Grid Padding="10" BackgroundColor="ForestGreen">
                <Grid.RowDefinitions>
                    <RowDefinition Height="30" />
                    <RowDefinition Height="50" />
                </Grid.RowDefinitions>
                <Label Text="ACCEPT TERMS" />
                <Label Grid.Row="1"
                     Text="By checking this, you agree to the Terms of Service and Privacy Policy." />
            </Grid>
        </DataTemplate>
    </ContentPage.Resources>		 
    <ScrollView>
        <VerticalStackLayout 
            Spacing="25" 
            Padding="30,0" 
            VerticalOptions="Center">
            <Button 
                x:Name="PlacementTargetHomePage"
                Text="PlacementTargetHomePage"
                SemanticProperties.Hint="Counts the number of times you click"
                Clicked="OnCounterClicked"
                HorizontalOptions="Center" />
        </VerticalStackLayout>
    </ScrollView>
 
</ContentPage>

private void OnCounterClicked(object sender, EventArgs e)
	{
        RadPopup tPopup = new RadPopup();
        tPopup.ContentTemplate = (DataTemplate)Resources["PopupTemplate"];
        tPopup.PlacementTarget = HomePage;
        tPopup.Placement = PlacementMode.Center;
        tPopup.IsOpen = true;
    }