How to fix Visual Studio C# WPF not supporting hint assist

Question

I'm relatively new to C# WPF programming and I've been trying to write a simple app using Material Design in xaml (using the MaterialDesignThemes nuget package).

I was trying to get a password box using the documentation provided by the MaterialDesignInXaml demo itself, but I keep getting this error

Hintassist is not supported in WPF

This is the piece of code that I try to run:

<TextBox
     VerticalAlignment="Top"
     materialDesign:HintAssist.HelperText="Helper text"
     materialDesign:HintAssist.Hint="Text (validated)"
     Style="{StaticResource MaterialDesignFilledTextBox}">

But obviously there's some error with the HintAssist feature here. This same error comes up in other features, too, like buttonassist, but it's mainly problematic in this situation.

Any help with this will be appreciated.