Make custom widgets independent of any WinUI framework concerns. Although one can add WinUI concerns to ther widget if they want to build a fully customized widget. In theory, it may also be possible to host a widget of WPF, Avalonia, or Blazor.

Hyperbar.Windows/Views/CommandView.xaml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="utf-8" ?>
-<Page
+<UserControl
     x:Class="Hyperbar.Windows.CommandView"
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
@@ -10,4 +10,4 @@
             </ItemsPanelTemplate>
         </ItemsControl.ItemsPanel>
     </ItemsControl>
-</Page>
+</UserControl>

Hyperbar.Windows/Views/CommandView.xaml.cs

@@ -3,7 +3,8 @@ using Microsoft.UI.Xaml.Input;
 
 namespace Hyperbar.Windows;
 
-public sealed partial class CommandView : Page
+public sealed partial class CommandView : 
+    UserControl
 {
     public CommandView() => InitializeComponent();
 

Hyperbar.Windows/Views/CommandViewModel.cs

@@ -9,7 +9,7 @@ public partial class CommandViewModel :
     ITemplatedViewModel
 {
     public CommandViewModel(ITemplateFactory templateFactory, 
-        IEnumerable<ICommandWidgetViewModel> commands)
+        IEnumerable<IWidgetViewModel> commands)
     {
         TemplateFactory = templateFactory;
         AddRange(commands);

Hyperbar.Windows/Views/WidgetView.xaml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<UserControl
+    x:Class="Hyperbar.Windows.WidgetView"
+    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
+    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
+    <Grid />
+</UserControl>

Hyperbar.Windows/Views/WidgetView.xaml.cs

@@ -0,0 +1,10 @@
+using Microsoft.UI.Xaml.Controls;
+
+namespace Hyperbar.Windows;
+
+public sealed partial class WidgetView :
+    UserControl,
+    IWidgetView
+{
+    public WidgetView() => InitializeComponent();
+}