I have XAML with an element like While using that in Unity 3D 2022.3.16 with Noesis 3.2.2 an error is shown in the Unity log:

[NOESIS/E] ...: Cannot set value for 'PathGeometry.FillRule', unable to convert 'Nonzero' to a valid value

That error can be removed simply by changing Nonzero to NonZero, so it's not a biggy.

However External\NoesisGUI\Runtime\API\Proxies\FillRule.cs specifies it as Nonzero so I guess it should be changed in one place or the other for consitency?

This is a bug, it should only accept the value 'Nonzero' as it is the name specified in the FillRule enum.
Could you please report it in our bugtracker?

Done.
https://www.noesisengine.com/bugs/view.php?id=3006

Thank you!