I ask because it seems all the other Noesis packages target .NET Standard.

This (targeting of .NET framework) causes a slight issue in .NET Core projects that use Noesis.GUI.Extensions since you get the ever ominous little yellow triangle of doom on your dependencies. I believe I could just download the extensions source and rebuild to target .NET Standard myself. However, that requires a bit of upkeep and I'm wondering if there is a reason you all have chosen to not target .NET Standard yourselves.

The Noesis.GUI.Extension nuget package is intended for use it only in the Blend WPF project, so you can write xaml that includes Noesis extension properties. This is why it targets .NET Framework. It would not be possible to use .NET Standard in this package because it depends on WPF classes for some extensions, and for the included Theme.

The rest of nuget packages are for the project that uses Noesis to render the UI, and Noesis.GUI package already provides all the extension properties, so there is no need in that project to also include the extensions package.

I hope this makes it clear.

I believe that's clear. .NET Core 3 is required for WPF, but .NET Core 3 only started in .NET Standard 2.1. However, .NET Standard 2.1 also kills off .NET Framework support. So, if you migrated there, you end up with the same problem in reverse and even worse since using .NET Core targeted releases from .NET Framework project is a real PITA, whereas the reverse is mostly moderately inconvenient.

However, since Microsoft is clearly trying to do away with the .NET Framework, might it make sense to add an additional package for Noesis.GUI.Extensions targeting .NET Core 3.0?

I'm going to revive this. I'm a bit confused myself by this, since WPF does live in .NET 5 now. The Framework version is no longer being developed.
So a move to .NET 5 as a target is in order here sooner or later I think?

Yes, this is something we will do in a future release. Created ticket #2000 to follow this issue.

Might want to think about the behaviors too. From what I know WPF moved the standard behavior stuff to the package
Microsoft.Xaml.Behaviors.Wpf, which has a different namespace in XAML. Would be good to eventually adjust that as well
so the Blend project can use that and not have a namespace collision with the Noesis part, which is still based on an older System.Windows.Interactivity.

We already support the use behaviors namespace in Noesis: viewtopic.php?f=14&t=1923&p=10947&hilit ... Wpf#p10947
But yes, we can also reference that new nuget instead of old interactivity, I updated the ticket #2000 to reflect that.

I thought this release3.0.9 supported .NET 5.0, so the discussion here and the ticket#2000 was resolved?

You are right, that ticket is already resolved and Noesis.GUI.Extensions nuget supports .NET and .NETCore as well as .NET Framework projects since 3.0.9 version. Thanks for pointing this out.