My recent WPF apps have generally used MahApps.Metro and its related material design extensions because the resulting UI looks a bit more modern (to my eyes, at least) than the WPF default.
This assembly targets Net 7 and has nullability enabled.
The library repository is available on github.
The change log is available here.
It provides some XAML resources which I've found helpful:
- CustomComboBox.xaml supports displaying error messages more neatly than is the case with the default WPF combobox control.
- MaterialDesignDropDownButton.xaml provides a somewhat nicer looking dropdown button than the one provided by the MahApps material design library.