.net core reference

I'm trying to port a .net framework app to .net core (3.1), so I get the packages from nuget helixtoolkit, helixtoolkit.core.wpf and helixtoolkit.core.sharpdx. But the regefence in xaml, that I copied here: http://docs.helix-toolkit.org/en/latest/wpf/getting-started.html#adding-the-toolkit-to-your-xaml is not correct. errors desappear if I reference  xmlns:HelixToolkit="http://helix-toolkit.org/wpf", but app not show anything and crash.What am I missing?