Trouble adding UniformGrid to MainPage.xaml forUnoPlatform ubuntu c# solution

[HowardPWeiss]

MainPage.xaml includes

<Page
    x:Class="SudokuUnoBlank.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:vm="using:SudokuUnoBlank.ViewModels"
    xmlns:models="using:SudokuUnoBlank.Models"
    xmlns:conv="using:SudokuUnoBlank.Converters"
    xmlns:local="using:SudokuUnoBlank"
    xmlns:primitives="using:Uno.CommunityToolkit.WinUI.UI.Controls.Primitives"
    Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">

    <!-- ✅ Converters -->
    <Page.Resources>
        <conv:NullToVisibilityConverter x:Key="NullToVisibilityConverter" />
        <conv:InverseNullToVisibilityConverter x:Key="InverseNullToVisibilityConverter" />
        <conv:BoolToColorConverter x:Key="BoolToColorConverter" />
    </Page.Resources>

    <!-- ✅ ViewModel -->
    <Page.DataContext>
        <vm:MainViewModel />
    </Page.DataContext>

    <!-- ✅ Sudoku Grid -->
    <Grid Background="White" Padding="12">
        <ItemsControl ItemsSource="{Binding Cells}">
            <ItemsControl.ItemsPanel>
                <ItemsPanelTemplate>
                    <primitives:UniformGrid Rows="9" Columns="9" />
                </ItemsPanelTemplate>
            </ItemsControl.ItemsPanel>

            <ItemsControl.ItemTemplate>
                <DataTemplate>
                    <Border BorderBrush="Black"
                            BorderThickness="0.6"
                            Margin="1"
                            Background="{Binding IsCellValid, Converter={StaticResource BoolToColorConverter}}">
                        <Grid>
                            <!-- ✅ Large number when Value exists -->
                            <TextBlock Text="{Binding Value}"
                                       FontSize="28"
                                       FontWeight="Bold"
                                       HorizontalAlignment="Center"
                                       VerticalAlignment="Center"
                                       Visibility="{Binding Value, Converter={StaticResource NullToVisibilityConverter}}"/>

                            <!-- ✅ 3×3 grid of possible values when Value is null -->
                            <primitives:UniformGrid Rows="3" Columns="3"
                                                    Visibility="{Binding Value, Converter={StaticResource InverseNullToVisibilityConverter}}">
                                <TextBlock Text="1" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[0], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="2" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[1], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="3" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[2], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="4" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[3], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="5" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[4], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="6" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[5], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="7" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[6], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="8" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[7], Converter={StaticResource BoolToColorConverter}}"/>
                                <TextBlock Text="9" FontSize="10" HorizontalAlignment="Center" VerticalAlignment="Center"
                                           Foreground="{Binding PossibleValues[8], Converter={StaticResource BoolToColorConverter}}"/>
                            </primitives:UniformGrid>
                        </Grid>
                    </Border>
                </DataTemplate>
            </ItemsControl.ItemTemplate>
        </ItemsControl>
    </Grid>
</Page>

.csproj file includes

Directory.Packages.Props include

dotnet list package

[net9.0-desktop1.0]:
Top-level Package Requested Resolved

CommunityToolkit.Mvvm (A) [8.4.0, ) 8.4.0
Microsoft.Extensions.Logging.Console (A) [9.0.9, ) 9.0.9
SkiaSharp.Skottie (A) [3.119.1, ) 3.119.1
SkiaSharp.Views.Uno.WinUI (A) [3.119.1, ) 3.119.1
Uno.CommunityToolkit.WinUI.UI.Controls.Primitives 7.1.204 7.1.204
Uno.Fonts.OpenSans (A) [2.7.1, ) 2.7.1
Uno.Resizetizer (A) [1.11.1, ) 1.11.1
Uno.Sdk.Extras (A) [6.1.1, ) 6.1.1
Uno.Settings.DevServer (A) [1.6.3, ) 1.6.3
Uno.UI.Adapter.Microsoft.Extensions.Logging (A) [6.3.62, ) 6.3.62
Uno.UI.HotDesign (A) [1.16.109, ) 1.16.109
Uno.WinUI (A) [6.3.62, ) 6.3.62
Uno.WinUI.DevServer (A) [6.3.62, ) 6.3.62
Uno.WinUI.Graphics2DSK (A) [6.3.62, ) 6.3.62
Uno.WinUI.Lottie (A) [6.3.62, ) 6.3.62
Uno.WinUI.Runtime.Skia.Linux.FrameBuffer (A) [6.3.62, ) 6.3.62
Uno.WinUI.Runtime.Skia.MacOS (A) [6.3.62, ) 6.3.62
Uno.WinUI.Runtime.Skia.Win32 (A) [6.3.62, ) 6.3.62
Uno.WinUI.Runtime.Skia.Wpf (A) [6.3.62, ) 6.3.62
Uno.WinUI.Runtime.Skia.X11 (A) [6.3.62, ) 6.3.62

dotnet build reports error

CSC : error UXAML0001: Processing failed for file /home/howard/ChatGPT/SudokuUnoBlank/SudokuUnoBlank/MainPage.xaml (System.InvalidOperationException: The type {using:Uno.CommunityToolkit.WinUI.UI.Controls.Primitives}UniformGrid could not be found

According to Nuget package, this package supports

• UniformGrid: Presents items in an evenly-spaced set of rows or columns to fill the total available display space.

How do I fix my project/build?