Workaround
For bottom position set the vertical offset to be the height of the page:
<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"
xmlns:local="clr-namespace:MauiApp10"
x:Name="page"
x:Class="MauiApp10.MainPage">
<Grid BackgroundColor="Beige" RowDefinitions="*" x:Name="grid">
<Grid.GestureRecognizers>
<TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped" />
</Grid.GestureRecognizers>
<telerik:RadPopup.Popup>
<telerik:RadPopup x:Name="popup"
VerticalOffset="{Binding Height, Source={x:Reference page}}" HorizontalOffset="500"
Placement="Bottom">
<telerik:RadBorder WidthRequest="200"
CornerRadius="8"
BackgroundColor="#F9F9F9"
BorderColor="#DFDFDF"
BorderThickness="1"
Padding="12">
<Button TextColor="Black"
Clicked="Button_Clicked"
Text="The .NET MAUI Popup supports useful properties, which enable you to position it depending on your requirements." />
</telerik:RadBorder>
</telerik:RadPopup>
</telerik:RadPopup.Popup>
</Grid>
</ContentPage>Regards,
Didi
Progress Telerik