TestWindow.xaml

<Fluent:RibbonWindow x:Class="FluentTest.TestWindow"
                     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                     xmlns:Fluent="clr-namespace:Fluent;assembly=Fluent"
                     xmlns:FluentTest="clr-namespace:FluentTest"
                     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
                     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
                     x:Name="window"
                     Title="{Binding WindowTitle, ElementName=TestContent}"
                     Width="1024"
                     Height="768"
                     MinWidth="80"
                     MinHeight="60"
                     DataContext="{Binding DataContext, ElementName=TestContent}"
                     FlowDirection="LeftToRight"
                     WindowState="Normal"
                     mc:Ignorable="d">
    <Fluent:RibbonWindow.LayoutTransform>
        <!-- todo: netcore => was using x:Reference before -->
        <ScaleTransform ScaleX="{Binding DataContext.Zoom, ElementName=TestContent}" ScaleY="{Binding DataContext.Zoom, ElementName=TestContent}" />
    </Fluent:RibbonWindow.LayoutTransform>
    <Fluent:RibbonWindow.WindowCommands>
        <Fluent:WindowCommands>
            <Button Style="{DynamicResource Fluent.Ribbon.Styles.WindowCommands.Button}"
                    Content="Test" />
        </Fluent:WindowCommands>
    </Fluent:RibbonWindow.WindowCommands>
    <FluentTest:TestContent x:Name="TestContent" />
</Fluent:RibbonWindow>