I have a Styling library with the ResourceDictionary like this:

<ResourceDictionary.MergedDictionaries>
        <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Controls.xaml" />
        <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Fonts.xaml" />
        <ResourceDictionary Source="pack://application:,,,/MahApps.Metro;component/Styles/Themes/Light.Cobalt.xaml" />
        <ResourceDictionary Source="pack://application:,,,/Xceed.Wpf.AvalonDock.Themes.Metro;component/Theme.xaml"/>
    </ResourceDictionary.MergedDictionaries>

After I upgraded my application from .net4 to .net5 and migrated to MahApps V2. I got the error:

FileNotFoundException: Could not load file or assembly 'Xceed.Wpf.AvalonDock.Themes.Metro, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.

This Metro theme is used to styling the Tab Item of my application, make it look like this:

But now since I get this error, I cannot style my Tab Item as desired anymore, and I need it to be remained the original style before the upgrade.
I’m really new in UI development and have no idea what to do, so could anyone give me some suggestions ?