Avalonia/samples/ControlCatalog/Pages/MenuPage.xaml

<UserControl xmlns="https://github.com/avaloniaui">
  <StackPanel Orientation="Vertical" Gap="4">
    <TextBlock Classes="h1">Menu</TextBlock>
    <TextBlock Classes="h2">A window menu</TextBlock>

        <StackPanel Orientation="Horizontal"
              Margin="0,16,0,0"
              HorizontalAlignment="Center"
              Gap="16">
            <Menu>
                <MenuItem Header="_First">
                    <MenuItem Header="Standard _Menu Item"/>
                    <Separator/>
                    <MenuItem Header="Menu with _Submenu">
                        <MenuItem Header="Submenu _1"/>
                        <MenuItem Header="Submenu _2"/>
                    </MenuItem>
                    <MenuItem Header="Menu Item with _Icon">
                        <MenuItem.Icon>
                            <Image Source="resm:ControlCatalog.Assets.github_icon.png"/>
                        </MenuItem.Icon>
                    </MenuItem>
                    <MenuItem Header="Menu Item with _Checkbox">
                        <MenuItem.Icon>
                            <CheckBox BorderThickness="0" IsHitTestVisible="False" IsChecked="True"/>
                        </MenuItem.Icon>
                    </MenuItem>
                </MenuItem>
                <MenuItem Header="_Second">
                    <MenuItem Header="Second _Menu Item"/>
                </MenuItem>
            </Menu>
        </StackPanel>
    </StackPanel>
</UserControl>