If you want something similar to the Telerik ScreenTip, you should try the built-in ToolTip.

<Button
    Content="Click"
    ToolTipService.Placement="Bottom">
    <ToolTipService.ToolTip>
        <Grid RowDefinitions="Auto,*">
            <TextBlock
                Grid.Row="0"
                FontWeight="SemiBold"
                Text="Some Title" />
            <TextBlock
                Grid.Row="1"
                Text="Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
                TextWrapping="Wrap" />
        </Grid>
    </ToolTipService.ToolTip>
</Button>

Here's another option using an AttachedProperty.

<Window
x:Class="TipTests.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:local="using:TipTests"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Grid>
<Button
local:ScreenTip.Description="Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
local:ScreenTip.Placement="Bottom"
local:ScreenTip.Title="LOREM IPSUM"
Content="Click" />
</Grid>
</Window>

ScreenTip.cs

using Microsoft.UI.Text;
using Microsoft.UI.Xaml;
using Microsoft.UI.Xaml.Controls;
using Microsoft.UI.Xaml.Controls.Primitives;

namespace TipTests;

public class ScreenTip
{
    public static readonly DependencyProperty TitleProperty =
        DependencyProperty.RegisterAttached(
            "Title",
            typeof(string),
            typeof(ScreenTip),
            new PropertyMetadata(string.Empty, OnTitlePropertyChanged));

    public static readonly DependencyProperty DescriptionProperty =
        DependencyProperty.RegisterAttached(
            "Description",
            typeof(string),
            typeof(ScreenTip),
            new PropertyMetadata(string.Empty, OnDescriptionPropertyChanged));

    public static readonly DependencyProperty PlacementProperty =
        DependencyProperty.RegisterAttached(
            "Placement",
            typeof(PlacementMode),
            typeof(ScreenTip),
            new PropertyMetadata(default, OnPlacementPropertyChanged));

    public static string GetTitle(DependencyObject obj) => (string)obj.GetValue(TitleProperty);

    public static void SetTitle(DependencyObject obj, string value) => obj.SetValue(TitleProperty, value);

    public static string GetDescription(DependencyObject obj) => (string)obj.GetValue(DescriptionProperty);

    public static void SetDescription(DependencyObject obj, string value) => obj.SetValue(DescriptionProperty, value);

    public static PlacementMode GetPlacement(DependencyObject obj) => (PlacementMode)obj.GetValue(PlacementProperty);

    public static void SetPlacement(DependencyObject obj, PlacementMode value) => obj.SetValue(PlacementProperty, value);

    private static void OnTitlePropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Tip tip = GetTip(d);
        tip.TitleTextBlock.Text = e.NewValue as string ?? string.Empty;
        tip.TitleTextBlock.FontWeight = FontWeights.SemiBold;

        // Getting the parent.
        if (d is Button parent)
        {
            // Do something.
        }
    }

    private static void OnDescriptionPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Tip tip = GetTip(d);
        tip.DescriptionTextBlock.Text = e.NewValue as string ?? string.Empty;
        tip.DescriptionTextBlock.TextWrapping = TextWrapping.Wrap;
    }

    private static void OnPlacementPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        if (e.NewValue is PlacementMode placement)
        {
            ToolTipService.SetPlacement(d, placement);
        }
    }

    private static Tip GetTip(DependencyObject dependencyObject)
    {
        if (ToolTipService.GetToolTip(dependencyObject) is not Tip tip)
        {
            tip = new Tip();
            ToolTipService.SetToolTip(dependencyObject, tip);
        }

        return tip;
    }

    private class Tip : Grid
    {
        public Tip()
        {
            this.RowDefinitions.Add(new RowDefinition
            {
                Height = new GridLength(0, GridUnitType.Auto)
            });

            Grid.SetRow(this.TitleTextBlock, 0);
            this.Children.Add(this.TitleTextBlock);

            this.RowDefinitions.Add(new RowDefinition
            {
                Height = new GridLength(0, GridUnitType.Star)
            });

            Grid.SetRow(this.DescriptionTextBlock, 1);
            this.Children.Add(this.DescriptionTextBlock);
        }

        public TextBlock TitleTextBlock { get; } = new();

        public TextBlock DescriptionTextBlock { get; } = new();
    }
}